“using namespace” in c++ headers [duplicate]

by

You should definitely NOT use using namespace in headers for precisely the reason you say, that it can unexpectedly change the meaning of code in any other files that include that header. There’s no way to undo a using namespace which is another reason it’s so dangerous. I typically just use grep or the like to make sure that using namespace isn’t being called out in headers rather than trying anything more complicated. Probably static code checkers flag this too.

The header should include just the headers that it needs to compile. An easy way to enforce this is to always include each source file’s own header as the first thing, before any other headers. Then the source file will fail to compile if the header isn’t self-contained. In some cases, for example referring to implementation-detail classes within a library, you can use forward declarations instead of #include because you have full control over the definition of such forward declared class.

I’m not sure I would call it common, but it definitely shows up once in a while, usually written by new programmers that aren’t aware of the negative consequences. Typically just a little education about the risks takes care of any issues since it’s relatively simple to fix.

More Related Contents:

  1. using namespace std; in a header file
  2. scope of using declaration within a namespace
  3. Should I include stddef.h or cstddef for size_t
  4. ‘clrscr()’ and ‘conio.h’ not working
  5. Why is “using namespace std;” considered bad practice?
  6. Why have header files and .cpp files? [closed]
  7. Using std Namespace
  8. How to properly overload the
  9. printf with std::string?
  10. What are inline namespaces for?
  11. How to read a CMake Variable in C++ source code
  12. How can a C++ header file include implementation?
  13. How to create two classes in C++ which use each other as data?
  14. Namespaces in C
  15. Why an unnamed namespace is a “superior” alternative to static? [duplicate]
  16. Tools to find included headers which are unused? [closed]
  17. Is it a good practice to define C++ functions inside header files? [duplicate]
  18. Can I write C++ code without headers (repetitive function declarations)?
  19. How can I “unuse” a namespace?
  20. Which headers in the C++ standard library are guaranteed to include another header?
  21. Writing function definition in header files in C++
  22. multiple definition error c++
  23. Why can’t we declare a namespace within a class?
  24. Why and how should I use namespaces in C++?
  25. Interesting behavior of compiler with namespaces
  26. :: without a namespace
  27. What is the use of “using namespace std”? [duplicate]
  28. extern “C” linkage inside C++ namespace?
  29. C++ Circular Dependency in Header Files
  30. Namespaces and Operator Overloading in C++

Leave a Comment