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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 determine determines if the implementation sets errno by checking whether math_errhandling & MATH_ERRNO is nonzero. For complex functions, the C Standard, subclause 7.3.2, paragraph 1, simply states that "an implementation may set errno but is not required to" [ISO/IEC 9899:2011].
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