tempnam - create pathname for temporary file

Syntax	#include <stdio.h> char *tempnam(const char *dir, const char *pfx);
Description	tempnam() generates a pathname that may be used for a temporary file. tempnam() allows the user to control the choice of a directory. dir points to the name of the directory in which the file is to be created. If the environment variable TMPDIR is set, the directory specified there is used; otherwise, the one named under *dir. If dir is a null pointer and the directory {P_tmpdir} does not name an accessible directory, the file names are generated with the directory name /tmp. If this is not accessible either, 0 is returned. P_tmpdir is defined in stdio.h as "/var/tmp" as the directory in which temporary files are created. Many applications prefer their temporary files to have specific initial letter sequences in their names. The pfx argument should be used for this. This argument may be a null pointer or point to a string of up to five bytes to be used as the first bytes in the name of the temporary file. The name component generated by tempnam() is made up of two parts: the first comprises three uppercase letters (AAA, BAA, ..., ZAA, ZBA, ..., ZZZ); the second consists of a letter and the last five characters of the process ID. If the process ID consists of less than five characters, it is padded to five characters with leading zeros. For example, a complete name produced would be: /var/tmp/AAAa00123. tempnam() uses malloc() to obtain space for the generated file name and returns a pointer to that area. Thus, any pointer value returned by tempnam() can serve as an argument to free() (see malloc()). If tempnam() cannot return the expected result for some reason, e.g. because malloc() failed or no appropriate directory could be found, a null pointer is returned. tempnam() will fail if not enough memory is available.
Return val.	Pointer to a string containing the generated pathname
		if successful.
	Null pointer	if an error occurs. errno is set to indicate the error.
	Null pointer	if /tmp is not accessible. errno remains unchanged
Errors	tempnam() will fail if:
	ENOMEM	There is not enough memory available for the new pathname.
	Extension
	EINVAL	tempnam() is not called from POSIX-environment, i.e. the PROGRAM-ENVIRONMENT variable is not set to SHELL. (End)
Notes	tempnam() is executed only for POSIX files. tempnam() generates a different pathname at each call. Files created using tempnam() and either fopen() or creat() are temporary only in the sense that they reside in a directory intended for temporary use, and their names are unique. It is the user's responsibility to remove a file when it is no longer needed. If this function is called more than {TMP_MAX} (defined in stdio.h) times in a single process, the names created earlier will be reused. Between the time a pathname is created and the file is opened, it is possible for some other process to create a file with the same name. However, this will not occur if the other process is using tempnam() or mktemp() and if the pathname is chosen so as to render duplication by other means unlikely.
See also	fopen(), free(), open(), tmpfile(), tmpnam(), unlink(), stdio.h.