This header was originally in the C standard library as<iso646.h>.
Compatibility header, in C definesalternative operator representations which are keywords in C++.
This means that in a conforming implementation, including this header has no effect.
In old or nonconforming compilers, using thealternative operator representations may still require including this header.
<ciso646> is removed in C++20. Corresponding<iso646.h> is still available in C++20.
Prior to C++20, including<ciso646> was sometimes used as a technique for obtaining definitions of implementation-specific library version macros without causing other effects. As of C++20, the header<version> was added for this purpose.
#include <ciso646>#ifdef _LIBCPP_VERSION#error Using LLVM libc++#elif __GLIBCXX__ // Note: only version 6.1 or newer define this in ciso646#error Using GNU libstdc++#elif _CPPLIB_VER // Note: used by Visual Studio#error Using Microsoft STL#else#error Using an unknown standard library#endif
Possible output:
main.cpp:7:2: error: Using Microsoft STL#error Using Microsoft STL ^1 error generated.
