clinuxmacosunix

Why is the isnumber() function present in certain distros of Unix but not in others?

I'm writing a small C program in which I call the isnumber() function. 

#include <ctype.h>

char c
if(isnumber(c)) 
    { foo }

This compiles without a problem on my Mac (OS X 10.8). However, when I upload it to a CentOS 6.x server, it won't compile. Furthermore, the OS X man page for isdigit() describes isnumber(), but the CentOS man page does not. It's as if it simply doesn't exist on the Linux box. Both the OS X man page for isdigit() and a general Unix man page for isdigit() have isnumber() listed as part of the C standard library libc, -lc. When I add -lc to the compile flags on Linux, it still won't compile.

Why is this function included in certain forms on Unix and not in others?

Solution

  • isnumber() is a BSDism, as can be seen in the HISTORY section of the linked man page:

    The isnumber() function appeared in 4.4BSD.

    And there OS X shows its heritage...

    Also there is a STANDARDS section that talks about isdigit but mutes about isnumber.

    Anyway, Linux, BSD or OS X man pages should not be considered authoritative about the C language, or even about the POSIX standard. For C read the C standard specification (easy to find around), and for POSIX you can read the OpenGroup web site.