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It is also difficult to check for math errors using {{errno}} because an implementation might not set it. For real functions, the programmer can testtell whether the implementation sets {{errno}} by checking whenwhether {{math_errhandling & MATH_ERRNO}} is nonzero. For complex functions, the C99 Section 7.3.2 simply states "an implementation may set {{errno}} but is not required to" \[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\].