How can I create a temporary file for writing in C++ on a Linux platform?

Question

In C++, on Linux, how can I write a function to return a temporary filename that I can then open for writing?

The filename should be as unique as possible, so that another process using the same function won't get the same name.

Answer 1

Use one of the standard library "mktemp" functions: mktemp/mkstemp/mkstemps/mkdtemp.

Edit: plain mktemp can be insecure - mkstemp is preferred.

Answer 2

tmpnam(), or anything that gives you a name is going to be vulnerable to race conditions. Use something designed for this purpose that returns a handle, such as tmpfile():

   #include <stdio.h>

   FILE *tmpfile(void);

Answer 3

The GNU libc manual discusses the various options available and their caveats:

http://www.gnu.org/s/libc/manual/html_node/Temporary-Files.html

Long story short, only mkstemp() or tmpfile() should be used, as others have mentioned.

Answer 4

man tmpfile

The tmpfile() function opens a unique temporary file in binary read/write (w+b) mode. The file will be automatically deleted when it is closed or the program terminates.ote

Answer 5

mktemp should work or else get one of the plenty of available libraries to generate a UUID.

Answer 6

The tmpnam() function in the C standard library is designed to solve just this problem. There's also tmpfile(), which returns an open file handle (and automatically deletes it when you close it).

Answer 7

You should simply check if the file you're trying to write to already exists. This is a locking problem. Files also have owners so if you're doing it right the wrong process will not be able to write to it.