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mktemp - make a unique temporary file name
#include <stdlib.h> char *mktemp(char *template);
The mktemp() function generates a unique temporary file name from template. The last six characters of template must be XXXXXX and these are replaced with a string that makes the filename unique. Since it will be modified, template must not be a string constant, but should be declared as a character array.
The mktemp() function returns NULL on error (template did not end in XXXXXX) and template otherwise. If the call was successful, the last six bytes of template will have been modified in such a way that the resulting name is unique (does not exist already). If the call was unsuccessful, template is made an empty string.
EINVAL The last six characters of template were not XXXXXX.
BSD 4.3. POSIX dictates tmpnam(3).
The prototype is in <unistd.h> for libc4, libc5, glibc1; glibc2 follows the Single Unix Specification and has the prototype in <stdlib.h>.
Never use mktemp(). Some implementations follow BSD 4.3 and replace XXXXXX by the current process id and a single letter, so that at most 26 different names can be returned. Since on the one hand the names are easy to guess, and on the other hand there is a race between testing whether the name exists and opening the file, every use of mktemp() is a security risk. The race is avoided by mkstemp(3).