What is the extension of a C++ file?

Since the C language sources usually have the extension .c and .h, in the beginning it was common for C++ source files to share the same extensions or use a distinct variation to clearly indicate the C++ code file. Today this is the practice, most C++ implementation files will use the .cpp extension and .h for the declaration of header files (the last one is still shared across most assembler and C compilers).
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