Macro to check C++ compiler and version

The C++ language specifies that the macro __cplusplus will be defined if a C++ compiler is being used to compile the code. This is a good way to compile C or C++ code depending on whether a C or a C++ compiler is being used. This can be used for example to hide C++ constructs in a header file that is shared between C and C++ source files.

For example:

#ifdef __cplusplus
// Write some C++ code here
#else
// Write some C code here
#endif

The value of the __cplusplus macro is set by the compiler based on the version of the C++ standard it supports or you are requesting it to apply.

Here is a list of C++ standards and their corresponding __cplusplus values:

• C++98: 199711L
• C++11: 201103L
• C++14: 201402L
• C++17: 201703L
• C++20: 202002L

This is a value set inside the compiler implementation and not in any C++ standard library header file. I found the above values in the GCC source code defined here.

References

• GCC Standard Predefined Macros