Section: POSIX Programmer's Manual (3P)
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.
--- create a name for a temporary file
char *tmpnam(char *s);
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 POSIX.1-2017 defers to the ISO C standard.
function shall generate a string that is a valid pathname that does not
name an existing file. The function is potentially capable of generating
different strings, but any or all of them may already be in use by
existing files and thus not be suitable return values.
function generates a different string each time it is called from the
same process, up to
times. If it is called more than
times, the behavior is implementation-defined.
The implementation shall behave as if no function defined in this volume of POSIX.1-2017,
function need not be thread-safe if called with a NULL parameter.
Upon successful completion,
shall return a pointer to a string. If no suitable string can be
function shall return a null pointer.
If the argument
is a null pointer,
shall leave its result in an internal static object and return a
pointer to that object. Subsequent calls to
may modify the same object. If the argument
is not a null pointer, it is presumed to point to an array of at least
shall write its result in that array and shall return the argument
as its value.
No errors are defined.
The following sections are informative.
Generating a Pathname
The following example generates a unique pathname and stores it in the
array pointed to by
ptr = tmpnam(pathname);
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
Applications should use the
functions instead of the obsolescent
function may be removed in a future version.
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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