Opens a temporary file. See the mkstemp() documentation on most UNIX-like systems.
The parameter is a string that should follow the rules for mkstemp() templates, i.e. contain the string "XXXXXX". g_mkstemp() is slightly more flexible than mkstemp() in that the sequence does not have to occur at the very end of the template. The X string will be modified to form the name of a file that didn't exist. The string should be in the GLib file name encoding. Most importantly, on Windows it should be in UTF-8.
A file handle (as from open()) to the file opened for reading and writing. The file is opened in binary mode on platforms where there is a difference. The file handle should be closed with close(). In case of errors, -1 is returned and errno will be set.