---
name: "tmpnam"
section: "3"
platform: "macos"
package: "Libc"
version: "1752.120.2"
release: "macOS 26.5"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/tmpnam"
---

# tmpnam(3)

temporary file routines

## NAME

**tempnam**, **tmpfile**, **tmpnam** – temporary file routines

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<stdio.h\>**

*FILE* *\**\

**tmpfile**(*void*);

*char* *\**\

**tmpnam**(*char \*s*);

*char* *\**\

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

## DESCRIPTION

The **tmpfile**() function returns a pointer to a stream associated with a file descriptor returned by the routine [mkstemp(3)](/mkstemp/3.md). The created file is unlinked before **tmpfile**() returns, causing the file to be automatically deleted when the last reference to it is closed. The file is opened with the access value ‘w+’. If the environment variable TMPDIR is defined, the file is created in the specified directory. The default location, if TMPDIR is not set, is */tmp*.

The **tmpnam**() function returns a pointer to a file name, in the P\_tmpdir directory, which did not reference an existing file at some indeterminate point in the past. P\_tmpdir is defined in the include file ⟨stdio.h⟩. If the argument *s* is non-NULL, the file name is copied to the buffer it references. Otherwise, the file name is copied to a static buffer. In either case, **tmpnam**() returns a pointer to the file name.

The buffer referenced by *s* is expected to be at least L\_tmpnam bytes in length. L\_tmpnam is defined in the include file ⟨stdio.h⟩.

The **tempnam**() function is similar to **tmpnam**(), but provides the ability to specify the directory which will contain the temporary file and the file name prefix.

The argument *dir* (if non-NULL), the directory P\_tmpdir, the environment variable TMPDIR (if set), the directory */tmp* and finally, the current directory, are tried, in the listed order, as directories in which to store the temporary file.

The argument *pfx*, if non-NULL, is used to specify a file name prefix, which will be the first part of the created file name. The **tempnam**() function allocates memory in which to store the file name; the returned pointer may be used as a subsequent argument to [free(3)](/free/3.md).

## RETURN VALUES

The **tmpfile**() function returns a pointer to an open file stream on success, and a NULL pointer on error.

The **tmpnam**() and **tempfile**() functions return a pointer to a file name on success, and a NULL pointer on error.

## ENVIRONMENT

- TMPDIR

  \[**tempnam**() only\] If set, the directory in which the temporary file is stored. TMPDIR is ignored for processes for which [issetugid(2)](/issetugid/2.md) is true.

## COMPATIBILITY

These interfaces are provided from System V and ANSI compatibility only.

Most historic implementations of these functions provide only a limited number of possible temporary file names (usually 26) before file names will start being recycled. System V implementations of these functions (and of [mktemp(3)](/mktemp/3.md)) use the [access(2)](/access/2.md) system call to determine whether or not the temporary file may be created. This has obvious ramifications for setuid or setgid programs, complicating the portable use of these interfaces in such programs.

The **tmpfile**() interface should not be used in software expected to be used on other systems if there is any possibility that the user does not wish the temporary file to be publicly readable and writable.

## ERRORS

The **tmpfile**() function may fail and set the global variable *errno* for any of the errors specified for the library functions [fdopen(3)](/fdopen/3.md) or [mkstemp(3)](/mkstemp/3.md).

The **tmpnam**() function may fail and set *errno* for any of the errors specified for the library function [mktemp(3)](/mktemp/3.md).

The **tempnam**() function may fail and set *errno* for any of the errors specified for the library functions [malloc(3)](/malloc/3.md) or [mktemp(3)](/mktemp/3.md).

## SECURITY CONSIDERATIONS

The **tmpnam**() and **tempnam**() functions are susceptible to a race condition occurring between the selection of the file name and the creation of the file, which allows malicious users to potentially overwrite arbitrary files in the system, depending on the level of privilege of the running program. Additionally, there is no means by which file permissions may be specified. It is strongly suggested that [mkstemp(3)](/mkstemp/3.md) be used in place of these functions. (See the FSA.)

## LEGACY DESCRIPTION

In legacy mode, the order directories are tried by the **tempnam**() function is different; the environment variable TMPDIR (if defined) is used first.

## SEE ALSO

[mkstemp(3)](/mkstemp/3.md), [mktemp(3)](/mktemp/3.md)

## STANDARDS

The **tmpfile**() and **tmpnam**() functions conform to ISO/IEC 9899:1990 (“ISO C90”).