# tempnam

## NAME



           tempnam - create a name for a temporary file
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <stdio.h>**
    
           **char *tempnam(const char ***_dir_**, const char ***_pfx_**);**
    
       Feature Test Macro Requirements for glibc (see
       feature_test_macros(7)):
    
           **tempnam**():
               Since glibc 2.19:
                   _DEFAULT_SOURCE
               glibc 2.19 and earlier:
                   _BSD_SOURCE || _SVID_SOURCE
    


## DESCRIPTION



           _Never use this function._  Use mkstemp(3) or tmpfile(3) instead.
    
           The **tempnam**() function returns a pointer to a string that is a
           valid filename, and such that a file with this name did not exist
           when **tempnam**() checked.  The filename suffix of the pathname
           generated will start with _pfx_ in case _pfx_ is a non-NULL string of
           at most five bytes.  The directory prefix part of the pathname
           generated is required to be "appropriate" (often that at least
           implies writable).
    
           Attempts to find an appropriate directory go through the following
           steps:
    
           (1)  In case the environment variable **TMPDIR** exists and contains
                the name of an appropriate directory, that is used.
    
           (2)  Otherwise, if the _dir_ argument is non-NULL and appropriate,
                it is used.
    
           (3)  Otherwise, _P_tmpdir_ (as defined in _< stdio.h>_) is used when
                appropriate.
    
           (4)  Finally an implementation-defined directory may be used.
    
           The string returned by **tempnam**() is allocated using malloc(3) and
           hence should be freed by free(3).
    


## RETURN VALUE



           On success, the **tempnam**() function returns a pointer to a unique
           temporary filename.  It returns NULL if a unique name cannot be
           generated, with _errno_ set to indicate the error.
    


## ERRORS



           **ENOMEM** Allocation of storage failed.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────┬───────────────┬─────────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────┼───────────────┼─────────────┤
           │ **tempnam**()                        │ Thread safety │ MT-Safe env │
           └──────────────────────────────────┴───────────────┴─────────────┘
    


## STANDARDS



           POSIX.1-2008.
    


## NOTES



           Although **tempnam**() generates names that are difficult to guess, it
           is nevertheless possible that between the time that **tempnam**()
           returns a pathname, and the time that the program opens it,
           another program might create that pathname using open(2), or
           create it as a symbolic link.  This can lead to security holes.
           To avoid such possibilities, use the open(2) **O_EXCL** flag to open
           the pathname.  Or better yet, use mkstemp(3) or tmpfile(3).
    
           SUSv2 does not mention the use of **TMPDIR** ; glibc will use it only
           when the program is not set-user-ID.  On SVr4, the directory used
           under **(4)** is _/tmp_ (and this is what glibc does).
    
           Because it dynamically allocates memory used to return the
           pathname, **tempnam**() is reentrant, and thus thread safe, unlike
           tmpnam(3).
    
           The **tempnam**() function generates a different string each time it
           is called, up to **TMP_MAX**(defined in _< stdio.h>_) times.  If it is
           called more than **TMP_MAX** times, the behavior is implementation
           defined.
    
           **tempnam**() uses at most the first five bytes from _pfx_.
    
           The glibc implementation of **tempnam**() fails with the error **EEXIST**
           upon failure to find a unique name.
    


## BUGS



           The precise meaning of "appropriate" is undefined; it is
           unspecified how accessibility of a directory is determined.
    


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