What's with *.cxx files instead of *.cpp?

[Mike Pliam]

I occasionally come across source code that contains a mixture of *.cpp and *.cxx files.

Why do people do that ? What's the point ? How are they different? They seem the same to me.

I get the feeling that such source code has been ported from Fortran or some other 'academic' language.

What's the scoop?

Mike

[Krishnaa]

CXX and CPP are same with VC++, aparently the C++ source files were supposed to be .c++ but as few file systems dont allow + in extension, then it is said that x was used to mimic +, that how it became .cXX, not anyway different though.

[SuperKoko]

I occasionally come across source code that contains a mixture of *.cpp and *.cxx files.

It is probably due to a project using libraries (in form of source code) that don't use the same naming convention the programmer(s) of the project.

There are at least four different extensions usable for C++ files:

• .C
  Not very popular since it requires a case-sensitive file system (otherwise, it would clash with old .c file names), and even a few modern OS are not case-sensitive.
• .c++
  Some OS or file systems don't support the + character in file names.
• .cpp
  That's very portable across file systems.
  But, it might be less consistent than .cxx
• .cxx
  Very portable across file systems (not more than .cpp)
  Using the name CXX for C++ is quite popular because CPP usually designates the C (and C++) pre-processor.
  For example, these environment variables/makefile macros
  
  • CPPFLAGS
    Represents the flags passed to the pre-processor.
  • CFLAGS
    Flags passed to the C compiler.
  • CXXFLAGS
    Flags passed to the C++ compiler.
  • LDFLAGS
    Flags passed to the linker.
  • CC
    The path to the C compiler.
  • CPP
    The path to the pre-processor.
  • CXX
    The path to the C++ compiler.
  • LD
    The path to the linker.
  
  That's why, with the above notations, it's very natural to give the .cxx extension to C++ files.

For headers, there are at least five extensions:

• .h
  Traditional C header files.
  Since the compiler doesn't do anything based on this extension, it can be used for C++ header files too.
  Furthermore, there are a lot of header files that are designed to be included by both C and C++ translation units.
  In that case, it's natural to give them this extension.
• .H, .hpp or .hxx
  That's very natural to give one of these extensions for C++ header files (being consistent with the name of C++ translation units).
  That's not a bad idea to use one of these name for pure C++ header files only (containing class definitions, or templates, or any other feature not supported by C).
• No extension
  That's internally used by a number of C++ compilers for iostream, vector, algorithm and all others new-style C++ headers.

There are probably other (less popular) extensions for headers.
Perhaps .cpp and .i

[Mike Pliam]

Thanks for the info.

I dont know squat about programming Unix systems, but I do believe that most of the *.cxx and *.hxx files that I have encountered were originally intended for use with Unix mak files. And academic institutions seem to gravitate to Unix. Because I can never get those mak files to work properly, I have developed a hostile, mistrusting attitute towards them.

Sorry. I realize this isnt a psychotherapy session.

Regards.

Mike

[NMTop40]

I use .hpp and .hxx differently. .hpp files are exported headers, .hxx are internal headers local only to the module.

.hh and .cc are also used - for auto-generated source. CORBA IDL compiler for example produces .cc and .hh files. It's useful when you see these headers to know that a program generated them.

.h is popular for headers even in C++ although it's possibly best reserved for C-compatible headers. Often used for entry points to DLL. In a shared-object, all the symbols are exported but you can still use a .h file to publish the entry points from a C-interface so that a C client can use the library. A .h file can also be used for declarations of enums and constants.