Status of __STDC_IEC_559__ with modern C compilers

Question

C99 added a macro __STDC_IEC_559__ which can be used to test if a compiler and standard library conform to the ISO/IEC/IEEE 60559 (or IEEE 754) standard.

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Answer 1

1. I believe __STDC_IEC_559__ relies on some library features and can't be defined solely by the compiler. See this post for some information. This is not uncommon for C -- the compiler and the C library must sometimes cooperate in order to implement the entire standard.

2. What you're asking depends on the compiler. I think you would have to have special knowledge of the compiler in order to decide this. In the specific case of GCC, it defines a macro to tell you. Search this node of the manual for __GCC_IEC_559.

3. Well... I don't know the answer to this one :-). The original post seems to indicate that, yes, GCC might define __GCC_IEC_559 if it intends to implement IEEE 754, even if it does not actually do so.