You can think of POSIX as a runtime standard for C, but for many reasons, some language/operating system providers decide to either not provide a determined function, change its parameters, its name or some criterion on how to handle the request.\nIf a certain operating system does support the full set of POSIX operations with the standard names, parameters and criteria, then they may certify that with IEEE.\nThat allows you to create a C program and, as long as you use only POSIX functions, it's bound to work correctly on any POSIX-conformant system.\n\nHope it helped! Ignacio.--
non POSIX-compatible C functions?