std::tmpfile

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Input/output library

I/O manipulators

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

strstreambuf (deprecated in C++98)

basic_syncbuf (C++20)

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 in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

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>
std::FILE* tmpfile();

Creates and opens a temporary file with a unique auto-generated filename.

The file is opened as a binary file for update (as by std::fopen with access mode "wb+"). At least TMP_MAX files may be opened during the lifetime of a program (this limit may be shared with std::tmpnam and may be further limited by FOPEN_MAX).

If the program closes the file, e.g. by executing std::fclose, the file is automatically deleted.

If the program terminates normally (by calling std::exit, returning from main, etc), all files that were opened by calling std::tmpfile are also automatically deleted.

If the program terminates abnormally, it is implementation-defined if these temporary files are deleted.

Parameters

(none)

Return value

The associated file stream or NULL if an error has occurred

Notes

On some implementations (e.g. Linux), this function actually creates, opens, and immediately deletes the file from the file system: as long as an open file descriptor to a deleted file is held by a program, the file exists, but since it was deleted, its name does not appear in any directory, so that no other process can open it. Once the file descriptor is closed, the space occupied by the file is reclaimed by the filesystem.

On some implementations (e.g. Windows), elevated privileges are required as the function may create the temporary file in a system directory.

Example

Run this code

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <filesystem>
namespace fs = std::filesystem;
 
int main()
{
    std::FILE* tmpf = std::tmpfile();
    std::fputs("Hello, world", tmpf);
    std::rewind(tmpf);
    char buf[6];
    std::fgets(buf, sizeof buf, tmpf);
    std::cout << buf << '\n';
 
    // Linux-specific method to display the tmpfile name
    std::cout << fs::read_symlink(
                     fs::path("/proc/self/fd") / std::to_string(fileno(tmpf))
                 ) << '\n';
}

Possible output:

Hello
"/tmp/tmpfBlY1lI (deleted)"

See also

tmpnam	returns a unique filename (function)
temp_directory_path (C++17)	returns a directory suitable for temporary files (function)