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### 4.67 `tmpnam`, `tempnam`—name for a temporary file

Synopsis

    #include <stdio.h>
    char *tmpnam(char *s);
    char *tempnam(char *dir, char *pfx);
    char *_tmpnam_r(struct _reent *reent, char *s);
    char *_tempnam_r(struct _reent *reent, char *dir, char *pfx);

Description
Use either of these functions to generate a name for a temporary file. The generated name is guaranteed to avoid collision with other files (for up to `TMP_MAX` calls of either function).

`tmpnam` generates file names with the value of `P_tmpdir` (defined in ‘`stdio.h`’) as the leading directory component of the path.

You can use the `tmpnam` argument s to specify a suitable area of memory for the generated filename; otherwise, you can call `tmpnam(NULL)` to use an internal static buffer.

`tempnam` allows you more control over the generated filename: you can use the argument dir to specify the path to a directory for temporary files, and you can use the argument pfx to specify a prefix for the base filename.

If dir is `NULL`, `tempnam` will attempt to use the value of environment variable `TMPDIR` instead; if there is no such value, `tempnam` uses the value of `P_tmpdir` (defined in ‘`stdio.h`’).

If you don’t need any particular prefix to the basename of temporary files, you can pass `NULL` as the pfx argument to `tempnam`.

`_tmpnam_r` and `_tempnam_r` are reentrant versions of `tmpnam` and `tempnam` respectively. The extra argument reent is a pointer to a reentrancy structure.

Warnings
The generated filenames are suitable for temporary files, but do not in themselves make files temporary. Files with these names must still be explicitly removed when you no longer want them.

If you supply your own data area s for `tmpnam`, you must ensure that it has room for at least `L_tmpnam` elements of type `char`.

Returns
Both `tmpnam` and `tempnam` return a pointer to the newly generated filename.

Portability
ANSI C requires `tmpnam`, but does not specify the use of `P_tmpdir`. The System V Interface Definition (Issue 2) requires both `tmpnam` and `tempnam`.

Supporting OS subroutines required: `close`, `fstat`, `getpid`, `isatty`, `lseek`, `open`, `read`, `sbrk`, `write`.

The global pointer `environ` is also required.

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