.C VS .Cc VS. .Cpp VS .Hpp VS .H VS .Cxx

.c vs .cc vs. .cpp vs .hpp vs .h vs .cxx

Historically, the first extensions used for C++ were .c and .h, exactly like for C. This caused practical problems, especially the .c which didn't allow build systems to easily differentiate C++ and C files.

Unix, on which C++ has been developed, has case sensitive file systems. So some used .C for C++ files. Other used .c++, .cc and .cxx. .C and .c++ have the problem that they aren't available on other file systems and their use quickly dropped. DOS and Windows C++ compilers tended to use .cpp, and some of them make the choice difficult, if not impossible, to configure. Portability consideration made that choice the most common, even outside MS-Windows.

Headers have used the corresponding .H, .h++, .hh, .hxx and .hpp. But unlike the main files, .h remains to this day a popular choice for C++ even with the disadvantage that it doesn't allow to know if the header can be included in C context or not. Standard headers now have no extension at all.

Additionally, some are using .ii, .ixx, .ipp, .inl for headers providing inline definitions and .txx, .tpp and .tpl for template definitions. Those are either included in the headers providing the definition, or manually in the contexts where they are needed.

Compilers and tools usually don't care about what extensions are used, but using an extension that they associate with C++ prevents the need to track out how to configure them so they correctly recognize the language used.

2017 edit: the experimental module support of Visual Studio recognize .ixx as a default extension for module interfaces, clang++ is recognizing .c++m, .cppm and .cxxm for the same purpose.

*.h or *.hpp for your class definitions

Here are a couple of reasons for having different naming of C vs C++ headers:

• Automatic code formatting, you might have different guidelines for formatting C and C++ code. If the headers are separated by extension you can set your editor to apply the appropriate formatting automatically
• Naming, I've been on projects where there were libraries written in C and then wrappers had been implemented in C++. Since the headers usually had similar names, i.e. Feature.h vs Feature.hpp, they were easy to tell apart.
• Inclusion, maybe your project has more appropriate versions available written in C++ but you are using the C version (see above point). If headers are named after the language they are implemented in you can easily spot all the C-headers and check for C++ versions.

Remember, C is not C++ and it can be very dangerous to mix and match unless you know what you are doing. Naming your sources appropriately helps you tell the languages apart.

C++ code file extension? What is the difference between .cc and .cpp

At the end of the day it doesn't matter because C++ compilers can deal with the files in either format. If it's a real issue within your team, flip a coin and move on to the actual work.

What is the difference between .cc and .cpp file suffix?

Conventions.

Historically, the suffix for a C++ source file was .C.
This caused a few problems the first time C++ was ported
to a system where case wasn't significant in the filename.

Different users adopted different solutions: .cc,
.cpp, .cxx and possibly others. Today, outside of the Unix
world, it's mostly .cpp. Unix seems to use .cc more often.

For headers, the situation is even more confusing: for whatever
reasons, the earliest C++ authors decided not to distinguish
between headers for C and for C++, and used .h.

This doesn't cause any problems if there is no C in the project, but when you
start having to deal with both, it's usually a good idea to
distinguish between the headers which can be used in C (.h)
and those which cannot (.hh or .hpp).

In addition, in C++, a lot of users (including myself) prefer keeping the template
sources and the inline functions in a separate file. Which,
while strictly speaking a header file, tends to get yet another
set of conventions (.inl, .tcc and probably a lot of
others).

In the case of headers it makes absolutely no difference to the compiler.

In the case of source files different endings will cause the compiler to assume a different
language. But this can normally be overridden, and I used .cc
with VC++ long before VC++ recognized it as C++.

.c vs .cc vs. .cpp vs .hpp vs .h vs .cxx

Historically, the first extensions used for C++ were .c and .h, exactly like for C. This caused practical problems, especially the .c which didn't allow build systems to easily differentiate C++ and C files.

Unix, on which C++ has been developed, has case sensitive file systems. So some used .C for C++ files. Other used .c++, .cc and .cxx. .C and .c++ have the problem that they aren't available on other file systems and their use quickly dropped. DOS and Windows C++ compilers tended to use .cpp, and some of them make the choice difficult, if not impossible, to configure. Portability consideration made that choice the most common, even outside MS-Windows.

Headers have used the corresponding .H, .h++, .hh, .hxx and .hpp. But unlike the main files, .h remains to this day a popular choice for C++ even with the disadvantage that it doesn't allow to know if the header can be included in C context or not. Standard headers now have no extension at all.

Additionally, some are using .ii, .ixx, .ipp, .inl for headers providing inline definitions and .txx, .tpp and .tpl for template definitions. Those are either included in the headers providing the definition, or manually in the contexts where they are needed.

Compilers and tools usually don't care about what extensions are used, but using an extension that they associate with C++ prevents the need to track out how to configure them so they correctly recognize the language used.

2017 edit: the experimental module support of Visual Studio recognize .ixx as a default extension for module interfaces, clang++ is recognizing .c++m, .cppm and .cxxm for the same purpose.

Correct C++ file extension

It's a matter of code conventions. These extensions are all interchangeable (as far as platforms are concerned). If you participate in an existing project, you should adhere to this project's conventions, otherwise just choose whatever you like.

Is there any reason Google uses the cc extension instead of cpp in their open source projects?

It's entirely a matter of personal preference, at least for the person(s) starting the project. Whatever you choose, be consistent.

Why have header files and .cpp files?

Well, the main reason would be for separating the interface from the implementation. The header declares "what" a class (or whatever is being implemented) will do, while the cpp file defines "how" it will perform those features.

This reduces dependencies so that code that uses the header doesn't necessarily need to know all the details of the implementation and any other classes/headers needed only for that. This will reduce compilation times and also the amount of recompilation needed when something in the implementation changes.

It's not perfect, and you would usually resort to techniques like the Pimpl Idiom to properly separate interface and implementation, but it's a good start.

What is the difference between a .cpp file and a .h file?

The C++ build system (compiler) knows no difference, so it's all one of conventions.

The convention is that .h files are declarations, and .cpp files are definitions.

That's why .h files are #included -- we include the declarations.

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