#include <stdio.h>char *tmpnam(char *s);
These functions generate file names that can safely be used for a temporary file.
The tmpnam() function always generates a file name using the path prefix defined as P_tmpdir in the <stdio.h> header. On Solaris systems, the default value for P_tmpdir is /var/tmp . If s is NULL , tmpnam() leaves its result in an internal static area and returns a pointer to that area. The next call to tmpnam() will destroy the contents of the area. If s is not NULL , it is assumed to be the address of an array of at least L_tmpnam bytes, where L_tmpnam is a constant defined in <stdio.h> ; tmpnam() places its result in that array and returns s .
The tmpnam_r() function has the same functionality as tmpnam() except that if s is a null pointer, the function returns NULL . This interface is as proposed in the POSIX.4a Draft #6 document, and is subject to change to be compliant to the standard when it is accepted.
The tempnam() function allows the user to control the choice of a directory. The argument dir points to the name of the directory in which the file is to be created. If dir is NULL or points to a string that is not a name for an appropriate directory, the path prefix defined as P_tmpdir in the <stdio.h> header is used. If that directory is not accessible, /tmp is used. If, however, the TMPDIR environment variable is set in the user's environment, its value is used as the temporary-file directory.
Many applications prefer that temporary files have certain initial character sequences in their names. The pfx argument may be NULL or point to a string of up to five characters to be used as the initial characters of the temporary-file name.
The tempnam() function uses malloc(3C) to allocate space for the constructed file name, and returns a pointer to this area. Any pointer value returned from tempnam() may serve as an argument to free(3C) (see malloc(3C) ). If tempnam() cannot return the expected result for any reason (for example, malloc(3C) failed), or if none of the above-mentioned attempts to find an appropriate directory was successful, a null pointer is returned. This function fails if there is not enough space.
These functions generate a different file name each time they are called.
Files created using these functions and either fopen(3C) or creat(2) are temporary only in the sense that they reside in a directory intended for temporary use, and their names are unique. It is the user's responsibility to remove the file when its use is ended.
If called more than TMP_MAX (defined in <stdio.h> ) times in a single process, these functions start recycling previously used names.
Between the time a file name is created and the file is opened, it is possible for some other process to create a file with the same name. This can never happen if that other process is using these functions or mktemp(3C) and the file names are chosen to render duplication by other means unlikely.
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|
|MT-Level||See NOTES below.|
The tmpnam() function is unsafe in multithreaded applications. The tempnam() function is safe in multithreaded applications and should be used instead.
When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should be used only with multithreaded applications.