std::tmpnam

 

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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

filename

-

pointer to the character array capable of holding at least L_tmpnam 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 <cstdio>
#include <iostream>
#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 (C++17)	returns a directory suitable for temporary files (function)
C documentation for tmpnam