NAME¶

std::tmpnam - std::tmpnam

Synopsis¶

Defined in header <cstdio>
char* tmpnam( char* filename );

Creates a unique filename that does not name a currently existing file, and stores
it in the character string pointed to by filename. The function is capable of
generating up to TMP_MAX of unique filenames, but some or all of them may already be
in use, and thus not suitable return values.

std::tmpnam modifies static state and is not required to be thread-safe.

Parameters¶

pointer to the character array capable of holding at least L_tmpnam
filename - bytes, to be used as a result buffer. If a null pointer is passed, a
pointer to an internal static buffer is returned.

Return value¶

filename if filename was not a null pointer. Otherwise a pointer to an internal
static buffer is returned. If no suitable filename can be generated, a null pointer
is returned.

Notes¶

Although the names generated by std::tmpnam are difficult to guess, it is possible
that a file with that name is created by another process between the moment
std::tmpnam returns and the moment this program attempts to use the returned name to
create a file. The standard function std::tmpfile and the POSIX function mkstemp do
not have this problem (creating a unique directory using only the standard C library
still requires the use of tmpnam).

POSIX systems additionally define the similarly named function tempnam, which offers
the choice of a directory (which defaults to the optionally defined macro P_tmpdir).

Example¶

// Run this code

#include <iostream>
#include <cstdio>
#include <string>

int main()
{
std::string name1 = std::tmpnam(nullptr);
std::cout << "temporary file name: " << name1 << '\n';

char name2[L_tmpnam];
if (std::tmpnam(name2)) {
std::cout << "temporary file name: " << name2 << '\n';
}
}

Possible output:¶

temporary file name: /tmp/fileDjwifs
temporary file name: /tmp/fileEv2bfW

See also¶

tmpfile creates and opens a temporary, auto-removing file
(function)
temp_directory_path returns a directory suitable for temporary files
(C++17) (function)