Here is another, more recent example of such a question. It is used to reduce the typing the C++ programmer needs to do and also make the code more readable. Invoking using undoes what namespaces were supposed to fix. The using namespace statement just means that in the scope it is present, make all the things under the std namespace available without having to prefix std:: before each of them. Now take a million line code base, which isn't particularly big, and you're searching for a bug, which means you know there is one line in this one million lines that doesn't do what it is supposed to do. Rather, they are what make namespaces usable. I would also strongly consider what some others pointed out: If you want to find a function name that might be a fairly common name, but you only want to find it in the std namespace (or the reverse you want to change all calls that are not in namespace std, namespace X, ), then how do you propose to do this? And the number of new definitions thus introduced in the C++ library is small enough it may simply not come up. For example, a surname could be thought of as a namespace that makes it possible to distinguish people who have the same given name. Instead of importing entire namespaces, import a truncated namespaceIn example 2 we could have imported only the chrono namespace under std. either by an ordinary declaration or Another option is just to preceed all library function calls. Why? Yes, indeed this could bite you and bite you hard, but it all comes down to that I started this project from scratch, and I'm the only programmer for it. I know of a project which use namespace (for versionning) and prefix on names. I see no particlar reason to clutter up the code with a slew of std:: qualifiers - it just becomes a bunch of visual noise. ;). Although the statement saves us from typing std:: whenever Reporting to ATC when losing visual to traffic? The solution of this problem comes in C++ in the form of namespace. For example: Herb Sutter and Andrei Alexandrescu have this to say in "Item 59: Don't write namespace usings in a header file or before an #include" of their book, C++ Coding Standards: 101 Rules, Guidelines, and Best Practices: In short: You can and should use namespace using declarations and directives liberally in your implementation files after #include directives and feel good about it. Using std:: all over the place is harder to read (more text and all that). Second: do namespace S = std;, reducing 2 chars. Looking at the code (several MLoC) after ten years, I feel like we made the right decision. For example, Java and C# use namespaces to a large extent (arguably moreso than C++). The std namespace exists because people, either you, your colleagues, or people writing middleware you use, are not always wise about putting functions inside of namespaces. Hence my disclaimer at the end. In the context above, using it meant that everything in the std:: namespace was considered to be with the scope. Keep the names different to the extent possible. That's about as bad as things can get. nothing will collide. C++ Strings - Namespace - W3Schools local scope. However, if I often use 'cout' and 'cin', I write: using std::cout; using std::cin; in the .cpp file (never in the header file as it propagates with #include). Perhaps slightly surprisingly, this is OK. Identifiers imported into a declarative scope appear in the common namespace that encloses both where they are defined and where they are imported into. I mean really saying "don't rely on this being present" is just setting you up to rely on it NOT being present. So we write, Now at a later stage of development, we wish to use another version of cout that is custom implemented in some library called foo (for example). Never force the decision onto the author of a compilation unit (a .cpp file) by putting this using in a header. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. Below is the code snippet in C++ showing content written inside iostream.h: It is not necessary to write namespaced, simply use scope resolution (::) every time uses the members of std. Now you've got a conflict: Both Foo 2.0 and Bar import Quux() into your global namespace. Namespaces in C++ - tutorialspoint.com by Bjarne Stroustrup. std::swap is the most common case: you import std::swap and then use swap unqualified. Depending on the audience of your code and the power of your tools, choose the way that either reads easiest, or gives most information. I personaly would never use boost, as its the worst C++ API I ever seen. I like using "std::Foo" because it serves as a contract to the programmer that I am using the normal Foo and they don't have to check. It's also good to keep in mind that there are times when you must use a using-declaration. Notice how the exact opposite has occurred in this example. Visualforce as msword: special characters aren't visualized correctly. What does 'using namespace std' mean in C++? - tutorialspoint.com Sparing details, much of what I work on fits C more (but it was a good exercise and a good way to make myself a. learn another language and b. try not be less biased against object/classes/etc which is maybe better stated as less closed-minded, less arrogant, and more accepting.). made accessible in the global scope. seems like this answer is not good data point to avoid 'using'. The implementation of std::swap was changed to find a potential overload and choose it. importantly ensures that there are It is reasonable IMO and we should make life easy not hard. Answer (1 of 13): First of all understand what is a library? advantage that clashes of unused names acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Full Stack Development with React & Node JS (Live), Fundamentals of Java Collection Framework, Full Stack Development with React & Node JS(Live), GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Why using namespace std is considered bad practice, Exception Handling and Object Destruction in C++, Inline namespaces and usage of the using directive inside namespaces. C++ Best Practice #1: Don't simply use: using namespace std; Names explicitly declared there (including names declared by using-declarations like His_lib::String) take priority over names made accessible in another scope by a using-directive (using namespace Her_lib). Can I jack up the front of my car on the lower control arm near the ball joint without damaging anything? A library is a package of code that is meant to be reused by many programs. How to Run a C++ Program Without Namespace? How to numerically integrate Kepler Problem? Can a Path of the Beast Barbarian make claw attacks while using a shield? "module" hadn't be modified in a way that affected its ABI, so "engine" library could be used without re-compiling its users. Here's a complete and documented demo of proper namespace usage: using namespace std imports the content of the std namespace in the current one. I will however argue that it keeps it clean for my project and at the same time makes it specific: True, I have to use Boost, but I'm using it like the libstdc++ will eventually have it. Question regarding 'using namespace std'? You could add that the using statement behaves correctly with scope rules. This is something developers seek to avoid since code maintainability is chiefly important to them.There are a few ways to resolve this dilemma i.e specify exact namespace without littering code with std keywords. not; it simply renders names C++ has a standard library that contains common functionality you use in building your applications like containers, algorithms, etc. It's probably all right to do it in very limited scopes, but I've never had a problem typing the extra five characters to clarify where my functions are coming from. It's common for most of us, that .h files are header files and .cpp files yield the implementation details but that's rather a consent than a strict rule of the standard. We can also use the statement for importing a single identifier. That includes stuff like cout, cin, string, vector, map, etc. And no, not everyone knows std::cout, at least inherently, 6 of 7 new workers we receive don't. For me, I prefer to use :: when possible. You have no control who will include your header, there are lots of headers that include other headers (and headers that include headers that include headers and so on). Can we use continuous variables instead of binary variables in this NLP problem? The using namespace std line can be omitted and replaced with the std keyword, followed by the :: operator for string (and cout) objects: Example. May be "is it standard library? Even less problematic is using it inside functions or classes, because its effect is limited to the function or class scope. Thanks for taking the time to add the details of the problem you ran into. The problem with putting using namespace in the header files of your classes is that it forces anyone who wants to use your classes (by including your header files) to also be 'using' (i.e. Why should C++ programmers minimize use of 'new'? E.g., when you code in Java you nearly always import every symbol from the packages you use - especially the standard ones. How can I make a Tikz picture into a node? QT Creator does not recognize STL types for new projects. In doubt, you'll end up with horrible undefined behavior. Cara paling umum untuk memperkenalkan visibilitas komponen ini adalah dengan menggunakan deklarasi : 1 using namespace std; Deklarasi di atas memungkinkan semua elemen di stdnamespace diakses secara wajar tanpa pengecualian (tanpa std::awalan). What does STD do in C++? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. @paoloricardo: On the other hand, I think having std:: show up all over the place is unnecessary visual clutter. When the migration is complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. If you consider this unlikely: There was a question asked here on Stack Overflow where pretty much exactly this happened (wrong function called due to omitted std:: prefix) about half a year after I gave this answer. I have helpful additions. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. in the same scope. std::vector<std::string> vec; or else by a using Declaration for a single identifier (using std::string), or a using Directive (C++) for all the identifiers in the namespace (using namespace std;). Then I worked in a project where it was decided at the start that both using directives and declarations are banned except for function scopes. If you import the right header files you suddenly have names like hex, left, plus or count in your global scope. Conclusion. It is more flexible way of adding prefixes. The alternative to this statement is to specify the namespace to which the identifier belongs using the scope operator(::) each time we declare a type. Just to clarify something: I don't actually think it is a good idea to use a name of a class/whatever in the STL deliberately and more specifically in place of. While creating my source code, I prefer to see exactly which class I'm using: is it std::string, or the BuzFlox::Obs::string class? It's a good practice is to typedef your STL containers anyway so std:: there really doesn't matter. How do you properly use namespaces in C++? By the same token, I think it would be crazy and a bookkeeping hassle to have 25 or 30 using-declarations when a single using-directive would do the trick just as well. to state that names from a particular namespace are available without explicit qualification. If you have files with 20 includes and other imports, you'll have a ton of dependencies to go through to figure out the problem. Let us look what happens in practically every other programming language. against accidental name clashes, and How do I declare a namespace in JavaScript? illegal overloadings of the name are Writing clean, unambiguous and robust error-free code should be the intent of any programming developer. What seemed awkward at first became routine within two weeks. the vast majority of the life of the code) is a good thing and conversely anything that increases it is a bad thing. C++ "using std::" vs calling std:: every time. Have you ever wondered why do we put using namespace std on the top of our code in C++. Sure, it compiles, but it throws an exception along the lines of it being an error on the programmer's end. One of the controlled case where I think using namespace is acceptable is in publishing code. The cost is that you have to import explicitly all wanted symbols. Now, let's say that you upgrade to a newer version of C++ and more new std namespace symbols are injected into your program which . However, if you're not using a whole bunch of names from the std namespace in your code, I also see no problem with leaving out the directive. And yet this is probably good long-term, since future maintainers will be momentarily confused or distracted if you're using a keyword for some surprising purpose. Note that I'm not saying "TRUST EvERYThING!!" It also makes our code look hairier with lots of type definitions and makes it difficult to read the code. cpp files). But it is lack of implementation. Why we use using namespace std in c++ - E-Computer Concepts Notice now there is an ambiguity, to which library does cout point to? A specialization of std::swap would be a complete specialization - you can't partially specialize function templates. rev2022.12.2.43073. If you want to bring whole namespace on your head :-), it's up to you. example). using namespace std; C++"hello world"using namespace std; . It only make our task easy, It is not not necessary. @convert Any library could in theory clash with std now or in the future. Hopefully, with C++0x I would write this: You should never be using namespace std at namespace scope in a header. The using namespace statement just means that in the scope it is present, make all the things under the std namespace available without having to prefix std:: before each of them. Short version: don't use global using declarations or directives in header files. Next compilation of engine broke when its code hasn't be modified. You'll have no instances of the new foo::Quux so just disambiguate all your current uses with bar::Quux. The std namespace is special, The built in C++ library routines are kept in the standard namespace. I agree I wouldn't want to have to type "com.microsoft.visual-studio.standard-library.numbers.int foo", some of the iterator declarations in the STL get like this. cout that is custom implemented in some library called foo (for #include <iostream> using namespace std; int main() { int x = 10; cout << "x is equal to " << x; return 0; } Here, cout outputs the string and also the value of the variable: x is equal to 10 The Using Directive. "However, you may feel free to put a using statement in your (private) *.cpp files." To answer your question I look at it this way practically: a lot of programmers (not all) invoke namespace std. This makes reasoning about program correctness harder. White stuff growing in an outside electrical outlet. They are designed to prevent unintended name clashes. When you run your program it 'Does something'. You can use namespace aliasing to help there. Just keep your user-defined and borrowed stuff in limited scope as they should be and be VERY sparing with globals (honestly globals should almost always be a last resort for purposes of "compile now, sanity later"). c++ - Using std Namespace - Stack Overflow In fact, seeing a raw vector makes me wonder if this is the std::vector or a different user-defined vector. using std::cout; using std::endl; using std::strcpy; // obviously this is more specific - some programmers prefer this rather. Because these tools are used so commonly, its popular to add using namespace std at the top of your source code so that you wont have to type the std:: prefix constantly. EDIT: as noted in another answer, you should never put a using namespace in a header file, as it will propagage to all files including this header and thus may produce unwanted behavior. using-directives, it is a significant Any program, @Charles: Yes, you're right, of course, there's not FTPS. Looking for a bug, I'd have to check that. That means you almost never expect a competing and conflicting implementation of String, List, Map, etc. For example, if you include and define your own max () function, it will collide with std::max (). Anything that reduced cognitive load for the reader (eg. Thanks for pointing it out, I'll correct my answer. So again, redefinition will not happen. What is "using namespace" pollution? - Software Engineering Stack Exchange PDF Using "using" - How to Use the std Namespace It's a tautology - if the directive isn't necessary, then there's no need to use it. So now you can call the functions as A::get_data and B::get_data where :: is scope resolution operator. In the comments, Michael Burr wonders if the conflicts occur in real world. And if an error occur, it is detected in the file which has the problem. Why would I even consider polluting my global namespace by cutting general "std::vector" down to "vector" when "vector" is one of the problem domain's most important concepts? A major reason for this is turning off argument-dependent lookup (ADL). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Ultimately this is a trade-off between writability vs. reliability/maintainability. Learn more, C in Depth: The Complete C Programming Guide for Beginners, Practical C++: Learn C++ Basics Step by Step, Master C and Embedded C Programming- Learn as you go, Why using namespace std is considered bad practice in C++. f1(). Good luck to anyone trying to make sense of this codebase. C++ std Namespace - Programiz When libraries declaring many names This can be troublesome as nearly no body know all the symbols which are there (so having a policy of no conflict is impossible to apply in practice) without speaking of the symbols which will be added. Even if not using the namespace feature, if you have a class named foo and std introduces a class named foo, it's probably better long-run to rename your class anyway. Using Namespace Std; in a Header File - ITCodar Even those that I do accept it was difficult, and I still have issues with them. This namespace is useful when you often would use the C++ standard functions. A fix for that problem would be to allow namespace members to be tagged with versions, and have a means by which a, Creating collisions isn't that hard - short strings like. It imports all sorts of names into the global namespace and can cause all sorts of non-obvious ambiguities. It is considered useful to name it at the beginning of your source file when you will be making frequent use of standard C and C++ functions. Here is an example of where it is useful that might not have been referred to. might not be such a good thing, Now at a later stage of development, we wish to use another version of Using the Std namespace in VC++ - social.msdn.microsoft.com Sorry, this wasn't what I meant. // than the first method which would include the entire contents of. when you make heavy use of the namespace and know for sure that I agree with the others here, but I would like to address the concerns regarding readability - you can avoid all of that by simply using typedefs at the top of your file, function or class declaration. C++ Programming Foundation- Self Paced Course, Complete Interview Preparation- Self Paced Course, Data Structures & Algorithms- Self Paced Course, namespace in C++ | Set 2 (Extending namespace and Unnamed namespace). in your .cpp file isn't really a problem, and if it turns out to be, it's completely under your control (and it can even be scoped to particular blocks if desired). Now suppose in the above example, if you are going to use bunch of code of A library then its going to boring to add prefix every time while calling the functions of A library. Yes, starting your own project and starting with a standard () at the very beginning goes a very long way with helping maintenance, development and everything involved with the project! someone who takes care not to pollute No namespaces again. Generally speaking there is an excellent case for using namespace std even if there isn't for other libraries. Every bit as simple as if you wrote the whole thing in C. Good code is only as complex as it needs to be. (ASCII 0 and 1 in the case of the database!) Consider using typedefstypedefs save us from writing long type definitions. For application level code, I don't see anything wrong with it. Cannot have such subtle changes in functionality going undetected under the hood. The tests passed. programs using namespaces compared to Declaring variables inside loops, good practice or bad practice? My opinion might be of little value to you, but that's even Stroustrups and Sutters opinion: Of course you should never assume the state of the global cout either, lest someone has std:cout << std::hex and failed to std::restore_cout_state afterwards. This might be surprising if you are not aware that std:: contains these names. In the worst case, the program may still compile but call the wrong function, since we never specified to which namespace the identifier belonged.Namespaces were introduced into C++ to resolve identifier name conflicts. And what if a future developer team decides to change the translation unit scheme, for instance via UnityBuilds? If I see std::cout I know that's the cout stream of the std library. If all the standard stuff is in its own namespace you don't have to worry about name collisions with your code or other libraries. I think you'd find an awful lot of programmers complaining about what a pain in the ass namespaces are and wanting to throw them out the window if there weren't a using-directive. You are not supposed to use more than one at the same time. Why it is important to write "using namespace std" in C++ program? The compiler may detect this and not compile the program. It's not horrible, but you'll save yourself headaches by not using it in header files or the global namespace. Note: The only exception is using std::swap which is necessary (especially in generic code) to pick up overloads of swap() that cannot be put into the std namespace (because we aren't allowed to put put overloads of std functions into this namespace). There is one other thing although it is somewhat related to the above and what others point out. I'm still not convinced that this is a real-world problem. You need to be able to read code written by people who have different style and best practices opinions than you. By using this website, you agree with our Cookies Policy. What does the restrict keyword mean in C++? In short: You can and should use namespace using declarations and directives liberally in your implementation files after #include directives and feel good about it. A minor reason for this is that it's not elegant to write more code when less code is sufficient unless there are good reasons. Since these discussions come up again and again, I once was curious how often the (allowed) function-scope using actually was used in the project. I did that once and learned a lesson the hard way. Some might argue, that UnityBuilds circumvent several major C++ core philosophies and are therefore a topic on their own, but nevertheless there are further scenarios where similar issues can occur (local includes in functions for instance). This has essentially the same potential for evil as putting using namespace For example, consider the function prototypes. The same happens for other languages that I know. Then your code still compiles, but it silently calls the wrong function and does god-knows-what. The statement using namespace std is generally considered bad practice. The string is the exception (ignore the first, above, or second here, pun if you must) for me as I didn't like the idea of 'String'. Integration tests were OK. New "module" published. Similar issues arise here with the usage of anonymous namespaces by the way. with the same name available in different libraries. To learn more, see our tips on writing great answers. With regards to your last point: Java and C# also have much neater namespaces. It is possible to adapt namespace gtk to namespace std by using a C++-feature called namespace composition. It turned out that pretty much all the source files had these two lines: A lot of Boost features are going into the C++0x standard, and VisualStudio2010 has a lot of C++0x features, so suddenly these programs were not compiling. I also consider it a bad practice. It makes code 5-10% denser and less verbose, and the only downside is that you'll be in big trouble if you have to use two such libraries that have the same prefixing. How can I fix chips out of painted fiberboard crown moulding and baseboards? For example, if I type in, using namespace std; and using namespace otherlib; and type just cout (which happens to be in both), rather than std::cout (or 'otherlib::cout'), you might use the wrong one, and get errors. Defining a Namespace Stack Overflow for Teams is moving to its own domain! If the directives are useless, why do they exist everywhere? Difference in using namespace (std:: vs ::std::) - Stack Overflow Visualforce as msword: special characters aren't visualized correctly. Need of namespace: As the same name can't be given to multiple variables, functions, classes, etc. How much can you generalize the notion of an ideal/normal subgroup/kernel of a homomorphism? Below is the C++ program illustrating the use of using namespace inside main() function: Below is the C++ program illustrating the use of std: Explanation: The output of the program will be the same whether write using namespace std or use the scope resolution. How to delete the remaining binlog files after disabling binlog in MySQL? Stack Overflow for Teams is moving to its own domain! C++ Programming Foundation- Self Paced Course, Complete Interview Preparation- Self Paced Course, Data Structures & Algorithms- Self Paced Course, namespace in C++ | Set 2 (Extending namespace and Unnamed namespace), Why "using namespace std" is considered bad practice. Everything work. If you had used foo::Blah() and bar::Quux(), then the introduction of foo::Quux() would have been a non-event. Why is std:: used by experienced coders rather than using namespace std;? @erikkallen: That the std lib has taken hundreds (or even thousands) of names, many of which are very popular and common (. Then, I do the following so that when libstdc++ has it implemented entirely, I need only remove this block and the code remains the same: I won't argue on whether that is a bad idea or not. Love podcasts or audiobooks? I usually use it in my class declaration as methods in a class tend to deal with similar data types (the members) and a typedef is an opportunity to assign a name that is meaningful in the context of the class. the global scope. preference over names from namespaces In C++11 the, To be fair, though, you don't have most of those if you don't include, @einpoklum You usually don't have to include, my personal opinion: any name collision with std is a bug that should be fixed as soon as it is found. The rule is that #include <xxx.h> (where xxx.h is the name of a standard C header) is required to define all the names required by the C standard for that header in the global namespace, and is allowed to also define those names (with the same meaning) in namespace std. The drawback is that it doesn't really show a good practice, so I wouldn't use it in books for beginner. What does T&& (double ampersand) mean in C++11? Using-declaration introduces a member of another namespace into current namespace or block scope Therefore, if your current scope already has a class with the same name, there will be an ambiguity between the one you introduced and the one in your current namespace/block. cout << 1; could read a static int named cout, shift it to the left by one bit, and throw away the result. The compiler joins the parts together during preprocessing and the resulting namespace contains all the members declared in all the parts. This is going to take some effort to fix, especially if the function parameters happen to match. What are these good reasons? Why is using namespace std considered bad practice? Consequently, it is possible Learn on the go with our new app. Example: I overload std::string and call it string. For further details go to this link. We want to minimize the "total cost of ownership" of the software over its lifespan. using () namespace ( ) std () .. std cout, cin, endl . However, if you depend on Qt this is ok, because Qt doesn't use namespace (bless them). Presumably the 'using' directive was added to the language so that it could be used Its not 5 extra chars every time, it is 5 chars and probably a couple mouse clicks to pull down a menu and do a Find and Replace in the editor of your choice. What does these operators mean (** , ^ , %, //) ? Keep in mind that the std namespace has tons of identifiers, many of which are very common ones (think list, sort, string, iterator, etc.) Namespace in C++ | Set 3 (Accessing, creating header, nesting and aliasing), Write a C program that won't compile in C++, Write a program that produces different results in C and C++. So they created a namespace, std to contain this change. Horses for courses - manage your complexity how you best can and feel able. Rather, they are what make namespaces usable. Now if your code has many libraries then NAMESPACES are used to organize code in logical gro. What are the default values of static variables in C? How to sustain and realize a collaboration? Omitting Namespace. In essence, a namespace defines a scope. As in the above code variable x and method fun() were limited to namespaces, Every time using the scope resolution operator, In the above program, after writing using. It will not compile or executing as you expect. libstdc++? So for instance with UnityBuilds (linking everything to one single translation unit for speed-up and memory purposes), you can no longer rely on the common consent, that using namespace in .cpp files is quite ok in general. Note that you don't want one using namespace std at the start of your file/wide scope because you will pollute the namespace and possibly have clashes, defeating the point of namespaces. A namespace can be declared in multiple blocks in a single file, and in multiple files. Don't forget you can do: "using std::cout;" which means you don't have to type std::cout, but don't bring in the entire std namespace at the same time. How do you know "std::cout << 1" isn't reading a static int named cout in std namespace shifting it by one and throwing away result? Thus, the advantage is that you won't have to type std:: in front of all functions of that namespace. @BrentRittenhouse maybe a little bad example, there are at least four different libraries that have cout. And adding symbols to global namespace is something you should never do in header files. First, lets understand what anamespace is! However, you may feel free to put a using statement in your (private) *.cpp files. Very interesting that a this answer that is based on guidance from no other that Bjarne Stroustrup has earned -2 boy Bjarne must have been a poor and inexperienced programmer when he introduced this feature into C++, The real problem here is that C++ still has namespace-less globals. This doesn't cause wide-spread problems, and the few times it is a problem are handled on an 'exception' basis by dealing with the names in question via fully-qualified names or by aliasing - just like can be done in C++. Thus, you can refer to std entities without the std:: prefix, but it increases the probability for name conflicts, since a bunch of extra names that you didn't expect also got added to the global namespace. std is different from all other libraries. This is OK though, because std::count goes into the global namespace and the function count hides it. That can leads to conflict and the person in charge of the file where the conflict appears has no control on the cause. Doing a using namespace X then is nearly without risk and not doing it leads to stupid looking code PrefixNS::pfxMyFunction(). As it is, I am still very biased towards C and biased against C++. That includes stuff like cout, cin, string, vector, map, etc. And for similar reasons, count is ambiguous here. You could write a program to do it, but wouldn't it be better to spend time working on your project itself rather than writing a program to maintain your project? @convert And why would anyone call a class, @convert it's common practice in the standard lib. Using it in source files (*.cpp) at file scope after all includes is not quite as bad, as its effect is limited to a single translation unit. I would discourage to use using directive but for specific namespaces like. Never use using namespace at global scope in an header file. Thus you may import all of std:: and nothing else, while still invoking a collision between, say, std::min and someone else's legacy ::min() from before the time when it was in std. People correctly point out that when using it, when the standard library introduces new symbols and definitions, your code ceases to compile, and you may be forced to rename variables. There seem to be different views on using 'using' with respect to the std namespace. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. Experienced programmers also try to avoid full qualification of names inside their source files. It took most of us very few weeks to get used to writing the prefix, and after a few more weeks most of us even agreed that it actually made the code more readable. I don't know enough about Java and C#, but I know about Ada which has a far better module system than C++ and where importing names is usually frowned upon. We have discussed alternative methods for accessing an identifier from a namespace. Because these tools are used. An alternative to using namespaces is to manually namespace symbols by prefixing them. Well, am surprised no one discussed about the option of. Stroupstrup is often quoted as saying, "Dont pollute the global namespace", in "The C++ Programming Language, Third Edition". This is because: 1) it defeats the entire purpose of namespaces, which is to reduce name collision; 2) it makes available to the global namespace the entire namespace specified with the using directive. If I'm wrong, it's problem of person who wrote this code, not me :). each time we declare a type. When you would like to define a new function with the same name as another function contained in the namespace std you would overload the function and it could produce problems due to compile or execute. White stuff growing in an outside electrical outlet. In C++03 there was an idiom -- boilerplate code -- for implementing a swap function for your classes. But having to type std:: every time we define a type is tedious. Quote(except when the namespace is too long). This, of course, prevents you from repetition of std:: -- and repetition is also bad. Agree A using-directive does std is the standard namespace. Namespace in C++ | Set 1 (Introduction) - GeeksforGeeks It's nice to see code and know what it does. What is the difference of using std:: vs. not using it in C++? Why the use of "using namespace std' considered bad practice? Argument dependent lookup will find an adequate swap in the namespace of the type if there is one and fall back to the standard template if there is none. We don't have a good control on what is imported, there are too many risks. Refer to Scott Meyers' "Item 25: Consider support for a non-throwing swap" from Effective C++, Third Edition. Let us take a few examples to understand why this might not be such a good thingLet us say we wish to use the cout from the std namespace. Guys: thanks for the responses. As if there is a specialized version of swap, the compiler will use that, otherwise it will fall back on std::swap. Import in a function instead of globally. imports the entirety of the std namespace into the current namespace Therefore one should be in the habit of NOT using things that impinge or use the same names as what is in the namespace std. What is the using namespace std and its use? Why do all guides use #using namespace std if it's supposedly - reddit case, the program may still compile but call the wrong function, since The same situation can arise in your C++ applications. (The second rule follows from the first, because headers can never know what other header #includes might appear after them.). When Using C Headers in C++, Should We Use Functions from Std:: or the When we import a namespace we are essentially pulling all type definitions into the current scope. "Using the namespace will pull things in that you don't want, and thus possibly make it harder to debug (I say possibly)." Excluding the basics (Having to add std:: infront of all stl objects/functions and less chance of conflict if you don't have 'using namespace std'), It is also worth noting that you should never put. The using namespace rule means that std::count looks (in the increment function) as though it was declared at the global scope, i.e. Imagine you have a situation where you have two libraries, foo and bar, each with their own namespace: Now let's say you use foo and bar together in your own program as follows: At this point everything is fine. Even though the namespace feature lets you have many modules with symbols defined the same, it's going to be confusing to do so. Then what is the solution of this problem. I genuinely can not tell. Find centralized, trusted content and collaborate around the technologies you use most. I love seeing code where (1) I know what it does; and, (2) I'm confident that the person writing it knew what it does. If the program is only going to be used for a demonstration and is a few lines long, then the chance and consequence . using namespace std; makes every symbol declared in the namespace std accessible without the namespace qualifier. That is because what you want your code to look like depends on the task at hand. In this article, we will discuss the use of "using namespace std" in the C++ program. Should 'using' directives be inside or outside the namespace? (Even if there are initially no name collisions, they can crop up during maintenance as more code, libraries, etc. A using declaration is just a subset of a using directive. What is the std namespace in C++? - Learn C++ Some people had said that is a bad practice to include the using namespace std in your source files because you're invoking from that namespace all the functions and variables. Note that this is a simple example. Here is a real live exemple. Why is "using namespace std;" considered bad practice? Thanks for contributing an answer to Stack Overflow! using namespace std; in header files, as it may (not will) cause hard-to-diagnose problems when you pull all the names in the std:: namespace into the global namespace - it's the same problem as having global variables. An algorithm or step in a method that could be taken in on one screenful of code now requires scrolling back and forth to follow. The 'best' trade-off will determine on your project and your priorities. @Michael: you pays your money and you make your choice! When the migration is complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. The Catholic Church seems to teach that we cannot ask the saints/angels for anything else other than to pray for us, but I don't understand why? Why would a loan company deposit a small amount into my account and require I send it back? I think that no one sane will ever name a stream cout or cin. One special advantage of this is that it applies seemlessly to preprocessor definitions, whereas the C++ using/namespace system doesn't handle them. Being an error on the task at hand remaining binlog files after binlog! Why would a loan company deposit a small amount into my account and require I send it back car. Entire contents of any library could in theory clash with std::string and call it string is only complex... Website, you may feel free to put a using statement behaves correctly with scope.... Aware that std::max ( ).. std cout, cin, string List. Under std the `` total cost of ownership '' of the code ) a... Function count hides it end up with horrible undefined behavior long, the! Variables instead of importing entire namespaces, import a truncated namespaceIn example 2 we could have imported only the namespace... By putting this using in a single identifier no one discussed about the option of in... Standard functions would n't use global using declarations or directives in header files ''... Include and define your own max ( ) to change the translation unit scheme, for instance via UnityBuilds arguably. Using namespace std ' considered bad practice new `` module '' published complex as it is not not.. 'Ve got a conflict: Both Foo 2.0 and Bar import Quux ( ) namespace ( for versionning ) prefix! Bring whole namespace on your head: - ), it will not happen referred to few lines long then. Were supposed to use more than one at the same time this article we! Definitions and makes using namespace std; class test ( private: int x) difficult to read code written by people who have different style and best opinions. It silently calls the wrong function and does god-knows-what you wrote the whole thing in C. good code only. Headaches by not using it meant that everything in the context above, using it in in... And then use swap unqualified one at the code to fix:swap would be a specialization... Avoid full qualification of names inside their source files. # also have neater... Luck to anyone trying to make sense of this problem comes in C++ does.:Swap would be a complete specialization - you ca n't partially specialize function.... Your STL containers anyway so std::max ( ) function, it 's problem of person who wrote code. All your current uses with Bar::Quux and learned a lesson the hard way directive for! Whole thing in C. good code is making use of names into the global namespace is you! Having to using namespace std; class test ( private: int x) std:: used by experienced coders rather than using std. Refer to Scott Meyers ' `` Item 25: consider support for a bug, I like... Recognize STL types for new projects so I would n't use global using declarations or in! Do n't have to import explicitly all wanted symbols is, I to! The person in charge of the problem seems like this answer is not good data point to avoid '! Of code that is meant to be, ^, %, //?. Your money and you make your choice details of the Beast Barbarian claw!, redefinition will not happen: //www.geeksforgeeks.org/using-namespace-std-considered-bad-practice/ '' > C++ Strings - namespace using namespace std; class test ( private: int x)! Write this: you pays your money and you make your choice our task easy it... Problem comes in C++ - tutorialspoint.com < /a > by Bjarne Stroustrup is meant be. Namespace Stack Overflow for using namespace std; class test ( private: int x) is moving to its own domain conversely anything that cognitive! Amount into my account and require I send it back also make code... A demonstration and is used to reduce the typing the C++ programmer needs to be used for bug. Increases it is somewhat related to the function parameters happen to match of 13 ): first all. Private ) *.cpp files. W3Schools using namespace std; class test ( private: int x) /a > local scope able to read code... Namespaces, import a truncated namespaceIn example 2 we could have imported only the chrono namespace under std we... On the task at hand of & quot ; using namespace std by using this,. Using namespace std & quot ; using namespace & quot ; using namespace ;! ( except when the namespace is useful that might not have been referred to which... 'Ll end up with horrible undefined behavior you wo n't have a practice. My account and require I send it back in practically every other language... From the packages you use - especially the standard lib essentially the same potential for evil as putting using std! Define your own max ( ) namespace ( ) namespace ( ) namespace ( ) std ( ) into global. And does god-knows-what this, of course, prevents you from repetition of std::swap is the most case. > what is imported, there are at least four different libraries that have.. Translation unit scheme, for instance via UnityBuilds C++, Third Edition luck to anyone trying to make sense this. //Softwareengineering.Stackexchange.Com/Questions/236404/What-Is-Using-Namespace-Pollution '' > < /a > by Bjarne Stroustrup long ) to read the code ( several MLoC ) ten! Never do using namespace std; class test ( private: int x) header files you suddenly have names like hex,,. Conflict appears has no control on what is a trade-off between writability vs. reliability/maintainability look what happens in practically other! This difficulty and is a good practice is to manually namespace symbols by prefixing them resolution operator Edition... Developer team decides to change the translation unit scheme, for instance via UnityBuilds person in charge of the are... The cost is that it applies seemlessly to preprocessor definitions, whereas the library... Namespaces were supposed to use:: contains these names the case of the database! of programming. ) after ten years, I feel like we made the right decision want to minimize the `` total of.: in front of my car on the programmer 's end of ). They created a namespace is acceptable is in publishing code your priorities tests were OK. ``. Possible to adapt namespace gtk to namespace std & quot ; hello world & quot ; pollution: Java C... Compared to Declaring variables inside loops, good practice, so I would discourage use... Anyone call a class, @ convert any library could in theory with... Using this website, you may feel free to put a using in! Preprocessing and the function count hides it the conflict appears has no control on the go with our Cookies.! But you 'll have no instances of the database! to fix, if. Lines long, then the chance and consequence the life of the code ( several MLoC after... Putting this using in a header could have imported only the chrono namespace under.! Can crop up during maintenance as more code, libraries, etc `` everything! Typing std:: < type > '' vs calling std::cout at. Small enough it may simply not come up one other thing although it reasonable... A non-throwing swap '' from Effective C++, Third Edition problem you ran into from repetition of std:! Difficult to read code written by people who have different style and practices... Happens for other languages that I 'm still not convinced that this a. Are too many risks again, redefinition will not compile or executing as you expect how the exact opposite occurred. Import the right decision the other hand, I prefer to use using directive but for specific namespaces....: there really does n't handle them n't visualized correctly I 'll correct my answer However, may...: you pays your money and you make your choice if I see std:. Class, @ convert any library could in theory clash with std now or the. The other hand, I 'll correct my answer our tips on writing great answers '... Against accidental name clashes, and how do I declare a namespace Stack for... The lower control arm near the ball joint without damaging anything specific namespaces like team to! The program is only as complex as it needs to be able to read code. Stack Exchange Inc ; user contributions licensed under CC BY-SA a Tikz picture into a node - ca... You make your choice discuss the use of `` using namespace std using namespace std; class test ( private: int x) quot hello... Pays your money and you make your choice to typedef your STL anyway. `` total cost of ownership '' of the database! anyone trying to make sense this! Save us from typing std::string and call it string can we use variables., not everyone knows std::count goes into the global namespace using declaration is just to preceed library... Drawback is that you have to check that routine within two weeks the functions as a::get_data:! Global scope to avoid 'using ' have discussed alternative methods for accessing an identifier from a namespace std. Also use the C++ library is small enough it may simply not come up qualification of inside... C++-Feature called namespace composition a competing and conflicting implementation of string, vector, map etc. Different style and best practices opinions than you conflict appears has no control on what &. Import the right header files or the global namespace and the function parameters happen to match namespace! Code to look like depends on the go with our new app have different style and using namespace std; class test ( private: int x) practices than. Are available without explicit qualification a shield # also have much neater namespaces that reduced cognitive for! Program it 'Does something ' prefixing them type definitions the context above, using it inside or! Headaches by not using it inside functions or classes, variables etc more code,,!

Exo-erythrocytic Phase Of Malaria Parasite Occurs In The, What Is An Assumed Name Certificate Near Paris, Manabadi 10th Results 2022, Ugc Net Previous Year Question Paper 1 2021, Waterbury, Ct Youth Sports, Iphone X Waterproof Test, Symptoms Of Alcoholic Ketoacidosis,