Can Clang warn me when I use non-standard functions provided by the GNU C Library?

Question

I am writing a C program on OS X and compiling it with clang. I am quite new to C and I have come to understand that some functions like getline() are useful but non-standard. I would like to be able to compile the program on a system where the GNU C Library is not available. Not knowing exactly what functions are non-standard, I am hoping there is a command-line switch for clang to warn me whenever I use such functions. Is there?

Output from clang --version:

Apple LLVM version 5.1 (clang-503.0.40)

Answer 1

You can use feature test macros (see also: XSH 2.2.1 POSIX.1 Symbols) to request visibility of only a particular set of standard interfaces. In particular,

-D_XOPEN_SOURCE=600

on the command line or

#define _XOPEN_SOURCE 600

should expose POSIX base plus the XSI option for the outdated 2001 version of POSIX (the latest OSX supports). If you want just base, without XSI, define _POSIX_C_SOURCE to 200112L.

Answer 2

There is no command line switch to say 'tell me if this is nonstandard'. The most common way of developing code that needs to be compatible across a variety of platforms is the gnu autotools suite, which gives you a configuration script which checks for various functionality and allows you to code around it, or have the system give up before going any further.