What is "XX" in CXX in the CMakeLists.txt cmake file

Question

What is "XX" in CXX in the CMakeLists.txt cmake file.
What is its significance.

Why is this “XX” not PP vs CPP file?

Answer 1

XX means “++” (each X is like a “plus” rotated 45 °), CXX means “C ++”.

Why " CXX "?

• " C++ " is impossible due to the limitations of macro definitions (they cannot contain + );
• “ CPP ” (for “C Plus Plus”) is commonly used to mean “ C P re P rocessor”.

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For example, in the GNU Makefile, you can define the following "variables":

• CPPFLAGS : additional flags for the C preprocessor (also used in C ++).
• CFLAGS : additional flags for the C compiler.
• CXXFLAGS : additional flags for the C ++ compiler.

(Usually you use CPPFLAGS and CFLAGS for project C and CPPFLAGS and CXXFLAGS for C ++ project.)

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See also Difference between CPPFLAGS and CXXFLAGS in GNU Make and CFLAGS vs CPPFLAGS .

Related: Fix C ++ file extension (and duplicate links).

Answer 2

Many file systems do not allow the + file names, so for many years to source files C ++ has several naming conventions, including the .cpp , .cc and .cxx .

CMake has a similar problem, as its macro language is built around strings that are not allowed to hold special characters such as + . This is just a limitation on getting the CMake analyzer to become too complex. So when they write CXX , what they really mean is just C++ .