#if defined __USE_SVID || defined __USE_XOPEN
/* Default path prefix for `tempnam' and `tmpnam'.  */
# define P_tmpdir       "/tmp"
#endif

                /* System V/ANSI C; this is the wrong way to do this, do *not* use these. */    
                #if __BSD_VISIBLE || __XPG_VISIBLE                                              
                #define P_tmpdir        "/tmp/"                                                 
                #endif

#include <stdlib.h>
#include <string.h>
#include <errno.h>

/* Compile-time constant, defaults to option -DTMPDIR=/tmp */
#ifndef TMPDIR
#define TMPDIR "/tmp"
#endif

/* Return a dynamically allocated string.
 * The string will always start with the temporary directory;
 * a slash is always appended to a non-empty directory string.
 * If non-NULL, the suffix will be appended to that.
 * The allocation is sized so that the string will always have
 * at least one end-of-string byte, and room for 'extra'
 * additional characters.
 * If successful, the function will return a pointer to the
 * string, and keep errno unchanged. Otherwise the function
 * will return NULL (with errno most likely ENOMEM).
*/
char *temporary(const char *const suffix, const size_t extra)
{
    const size_t suffix_len = (suffix) ? strlen(suffix) : 0;
    size_t       chars, prefix_len = 0;
    const char  *prefix;
    char        *string, *s;
    int          saved_errno;

    saved_errno = errno;

    prefix = getenv("TMPDIR");
    if (!prefix)
        prefix = TMPDIR;

    if (prefix)
        prefix_len = strlen(prefix);

    chars = prefix_len + 1 + suffix_len + extra + 1;
    string = malloc(chars);
    if (!string) {
        errno = ENOMEM;
        return NULL;
    }

    memset(string + prefix_len + suffix_len, 0, 2 + extra);

    s = string;

    if (prefix_len > (size_t)0) {
        memcpy(s, prefix, prefix_len);
        s += prefix_len;
        if (s[-1] != '/')
            *(s++) = '/';
    }

    if (suffix_len > (size_t)0) {
        memcpy(s, suffix, suffix_len);
        s += suffix_len;
    }

    /* We already set the EOS using the memset() above. */
    errno = saved_errno;
    return string;
}