How can I determine if the operating system is POSIX in C?

Question

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Answer 1

Here is what I ended up with:

#include 
/*
NAME
    basename -- return pointer to last component of a pathname

Distribution: This function is in the public domain. 

Origin of function:
http://www.koders.com/c/fidEB79B7607A210C3BB7B813E793465F9D469AE912.aspx


SYNOPSIS
    char *basename (const char *name)

DESCRIPTION
    Given a pointer to a string containing a typical pathname
    (/usr/src/cmd/ls/ls.c for example), returns a pointer to the
    last component of the pathname ("ls.c" in this case).

Restrictions:
    Presumes a UNIX or DOS/Windows style path with UNIX or DOS/Windows 
    style separators.
*/

/*
NAME:
    basename: 

Function:
    return pointer to last component of a pathname

Distribution: 
    This function is in the public domain. 

Origin of function:
    http://www.koders.com/c/fidEB79B7607A210C3BB7B813E793465F9D469AE912.aspx


SYNOPSIS:
    char *basename (const char *name)

DESCRIPTION:
    Given a pointer to a string containing a typical pathname
    (/usr/src/cmd/ls/ls.c for example), returns a pointer to the
    last component of the pathname ("ls.c" in this case).

Restrictions:
    Presumes a UNIX or DOS/Windows style path with UNIX or
    DOS/Windows style separators.
    Windows volumes are only a-zA-Z.
    The original code suggests ISALPHA.

*/

char * basename (const char *name)
{
const char *base;
// predefined OS symbols
// http://sourceforge.net/apps/mediawiki/predef/index.php?title=Operating_Systems#UNIX_Environment

#ifndef DIR_SEPARATOR
#  define DIR_SEPARATOR '/'
#endif

#ifndef DIR_SEPARATOR_2 
#  define DIR_SEPARATOR_2 '\\'
#endif

// Check if we are running Unix like os
//   else assume Windows.  Note if we guess wrong, it's not
//   so bad because Windows includes the Unix separator.
#if defined (__unix__) || (defined (__APPLE__) && defined (__MACH__))
#  define IS_DIR_SEPARATOR(ch) ((ch) == DIR_SEPARATOR)
#else
#  define IS_DIR_SEPARATOR(ch) \
(((ch) == DIR_SEPARATOR) || ((ch) == DIR_SEPARATOR_2))
/* Skip over the disk name in MSDOS pathnames. */
if (isalpha(name[0]) && name[1] == ':') 
    name += 2;
#endif


for (base = name; *name; name++)
    {
    if (IS_DIR_SEPARATOR (*name))
        {
        base = name + 1;
        }
    }
return (char *) base;
}




int main (int argc, const char * argv[]) {
    /* Return the basename of a pathname. */


#define S1 "/usr/src/cmd/ls/ls.c"
#define S2 "/usr/src/cmd/ls/abc"
#define S3 "a:/usr/src/cmd/ls/def"
#define S4 "ghi"
#define S5 "jkl.txt"
#define S6 "d:\\usr\\src\\cmd\\mno.txt"
#define S7 "d:pqm.txt"

printf(S1 "  \t is %s\n",basename(S1));
printf(S2 "  \t is %s\n",basename(S2));
printf(S3 "  \t is %s\n",basename(S3));
printf(S4 "  \t is %s\n",basename(S4));
printf(S5 "  \t is %s\n",basename(S5));
printf(S6 "  \t is %s\n",basename(S6));
printf(S7 "  \t is %s\n",basename(S7));
    return 0;

}