warning: the use of `tmpnam' is dangerous, better use `mkstemp'

Question

(Note: This is not a duplicate question)

I'm using the libc function tmpnam, and getting the following warning:

warning: the use of 'tmpnam' is dangerous, better use 'mkstemp'

My question isn't "how to disable the warning", but rather "what function should I be using instead"? mkstemp doesn't help, because I'm not trying to create a temporary file - I'm creating a temporary directory. And AFAIK, there isn't an API function for that.

So if I'm not supposed to use tmpnam, what am I supposed to use?

Solution

You're looking for mkdtemp:

mkdtemp - create a unique temporary directory

e.g.,

#include <stdlib.h>
#include <string.h>
...
char templatebuf[80];
char *mkdirectory = mkdtemp(strcpy(templatebuf, "/tmp/mkprogXXXXXX"));

using strcpy to ensure the parameter passed to mkdtemp is writable (c89), or

#include <stdlib.h>
...
char templatebuf[] = "/tmp/mkprogXXXXXX";
char *mkdirectory = mkdtemp(templatebuf);

with c99.

Since the feature is "new" (only standardized within the past ten years, though provided in the mid-1990s on Linux), you need to turn the feature on in the header files with a preprocessor definition (which may differ from one platform to another). The simplest for Linux is to define _GNU_SOURCE, e.g.,

gcc -D_GNU_SOURCE -o foo foo.c