std::tmpnam

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

istrstream (deprecated)

ostrstream (deprecated)

strstream (deprecated)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

C-style I/O

Functions
File access
fopen freopen fclose fflush	fwide setbuf setvbuf
Direct input/output
fread
fwrite
Unformatted input/output
fgetc fgets fputc fputs getchar gets (until C++14) putchar puts ungetc	fgetwc fgetws fputwc fputws getwchar putwchar ungetwc
Formatted input/output
scanffscanfsscanf vscanfvfscanfvsscanf (C++11)(C++11)(C++11) printffprintfsprintfsnprintf (C++11) vprintfvfprintfvsprintfvsnprintf (C++11)	wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C++11)(C++11)(C++11) wprintffwprintfswprintf vwprintfvfwprintfvswprintf
File positioning
ftell
fgetpos
fseek
fsetpos
rewind
Error handling
clearerr
feof
ferror
perror
Operations on files
remove
rename
tmpfile
tmpnam

 

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

Creates an 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 NULL. Otherwise a pointer to an internal static buffer is returned. If no suitable filename can be generated, NULL 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)
C documentation for tmpnam