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tempnam - Man Page

create a name for a temporary file


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <stdio.h>

char *tempnam(const char *dir, const char *pfx);


The tempnam() function shall generate a pathname that may be used for a temporary file.

The tempnam() function allows the user to control the choice of a directory. The dir argument points to the name of the directory in which the file is to be created. If dir is a null pointer or points to a string which is not a name for an appropriate directory, the path prefix defined as P_tmpdir in the <stdio.h> header shall be used. If that directory is not accessible, an implementation-defined directory may be used.

Many applications prefer their temporary files to have certain initial letter sequences in their names. The pfx argument should be used for this. This argument may be a null pointer or point to a string of up to five bytes to be used as the beginning of the filename.

Some implementations of tempnam() may use tmpnam() internally. On such implementations, if called more than {TMP_MAX} times in a single process, the behavior is implementation-defined.

Return Value

Upon successful completion, tempnam() shall allocate space for a string, put the generated pathname in that space, and return a pointer to it. The pointer shall be suitable for use in a subsequent call to free(). Otherwise, it shall return a null pointer and set errno to indicate the error.


The tempnam() function shall fail if:


Insufficient storage space is available.

The following sections are informative.


Generating a Pathname

The following example generates a pathname for a temporary file in directory /tmp, with the prefix file. After the pathname has been created, the call to free() deallocates the space used to store the pathname.

#include <stdio.h>
#include <stdlib.h>
const char *directory = "/tmp";
const char *fileprefix = "file";
char *file;

file = tempnam(directory, fileprefix);

Application Usage

This function only creates pathnames. It is the application's responsibility to create and remove the files. Between the time a pathname is created and the file is opened, it is possible for some other process to create a file with the same name. Applications may find tmpfile() more useful.

Applications should use the tmpfile(), mkdtemp(), or mkstemp() functions instead of the obsolescent tempnam() function.



Future Directions

The tempnam() function may be removed in a future version.

See Also

fopen(), free(), mkdtemp(), open(), tmpfile(), tmpnam(), unlink()

The Base Definitions volume of POSIX.1-2017, <stdio.h>

Referenced By

stdio.h(0p), tmpnam(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual