Not to be trite, but I doubt particularly many people have trouble with this. GCC 4.7 is a very long time to have gone without updates. Note that GCC 5 switche

Not to be trite, but I doubt particularly many people have trouble with this. GCC 4.7 is a very long time to have gone without updates. Note that GCC 5 switched from c99 by default to c11 by default. This isn't "just" a compiler flag, and it's not a GCC problem either, you'll have the same problem in clang or ICC. Try upgrading and compiling with -std=c99. (or -std=gnu99 if that's your thing) You might find that gcc-9 works if you feed it the right standard of C. Compiler updates occasionally remove certain definitions from headers that aren't supposed to contain those definitions. For instance, lots of headers contain the definition for size_t, but only stddef.h is required to. Occasionally an update will hit that removes it from I dunno, rand.h or whatever. This is a good thing; headers shouldn't contain a bunch of extra crap in then. In those cases, it's because your code was always broken, not that the compiler upgrade broke it. Blaming the compiler in that case is like blaming QA. Which, to be fair, it was QA's fault.