The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


tmpfile - create a temporary file


#include <stdio.h>

FILE *tmpfile(void);


[CX] [Option Start] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard. [Option End]

The tmpfile() function shall create a temporary file and open a corresponding stream. The file shall be automatically deleted when all references to the file are closed. The file is opened as in fopen() for update (w+).

[CX] [Option Start] In some implementations, a permanent file may be left behind if the process calling tmpfile() is killed while it is processing a call to tmpfile().

An error message may be written to standard error if the stream cannot be opened. [Option End]


Upon successful completion, tmpfile() shall return a pointer to the stream of the file that is created. Otherwise, it shall return a null pointer [CX] [Option Start]  and set errno to indicate the error. [Option End]


The tmpfile() function shall fail if:

[CX] [Option Start] A signal was caught during tmpfile(). [Option End]
[CX] [Option Start] {OPEN_MAX} file descriptors are currently open in the calling process. [Option End]
[CX] [Option Start] The maximum allowable number of files is currently open in the system. [Option End]
[CX] [Option Start] The directory or file system which would contain the new file cannot be expanded. [Option End]
[CX] [Option Start] The file is a regular file and the size of the file cannot be represented correctly in an object of type off_t. [Option End]

The tmpfile() function may fail if:

[CX] [Option Start] {FOPEN_MAX} streams are currently open in the calling process. [Option End]
[CX] [Option Start] Insufficient storage space is available. [Option End]

The following sections are informative.


Creating a Temporary File

The following example creates a temporary file for update, and returns a pointer to a stream for the created file in the fp variable.

#include <stdio.h>
FILE *fp;

fp = tmpfile ();


It should be possible to open at least {TMP_MAX} temporary files during the lifetime of the program (this limit may be shared with tmpnam()) and there should be no limit on the number simultaneously open other than this limit and any limit on the number of open files ( {FOPEN_MAX}).






fopen(), tmpnam(), unlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>


First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 5

Large File Summit extensions are added.

The last two paragraphs of the DESCRIPTION were included as APPLICATION USAGE notes in previous issues.

Issue 6

Extensions beyond the ISO C standard are marked.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The APPLICATION USAGE section is added for alignment with the ISO/IEC 9899:1999 standard.

End of informative text.

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