Cross-platform compatibility of dprintf
c, conditional-compilation, linux, posix
Solution
Looks like `dprintf()` is actually in POSIX.1-2008 (with the semantics you want), so you can do this:
#if !defined(__GLIBC__) && _POSIX_C_SOURCE < 200809
#error "dprintf may not exist, or may be wrong"
#endif
`__GLIBC__` is defined if you're using a gnu build system. This is probably as safe as you can be without writing a small test program.
Problem
Linux has this nice function `dprintf`: The functions `dprintf()` and `vdprintf()` (as found in the glibc2 library) are exact analogues of `fprintf()` and `vfprintf()`, except that they output to a file descriptor fd instead of to a given stream. however as that same source points out: These functions are GNU extensions, not in C or POSIX. Clearly, the names were badly chosen. Many systems (like MacOS) have incompatible functions called `dprintf()`, usually some debugging version of `printf()`, perhaps with a prototype like ``` void dprintf (int level, const char *format, ...); ``` where the first parameter is a debugging level (and output is to `stderr`). Moreover, `dprintf()` (or `DPRINTF`) is also a popular macro name for a debugging `printf`. So, probably, it is better to avoid this function in programs intended to be portable. My question How can I make a setup that will safely call the `dprintf` that I want, if it exists, or fail to compile with some reasonably sane error message if that function doesn't exist? I guess I'd do something like this: ``` #ifdef SOMETHING #define Dprintf dprintf #else #error "no dprintf" #endif ``` but I don't know what `SOMETHING` should be. I guess I could restrict it to just Linux but could I make it looser?