DOCERR: tmpfile() Creates a Temporary File in the Root Dir

• The C Run-time (CRT) included with: - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 4.1,

       5.0
  

The Microsoft C run-time library function tmpfile() creates a temporary file in the root directory of the current drive. This file has read/write access and is automatically deleted when the file is closed.

The documentation for this function implies that the file will be created in the current working directory. This is not the case; the file will exist only in the root directory. To create a temporary file in a different directory, use the functions tmpnam() or tempnam() in conjunction with fopen().

Some obscure side effects can occur on some systems as a result of tmpfile() creating a file in the root directory. On a network, you must have read/write privileges for the root directory of your current drive. Without these rights, tmpfile() will fail to open the temporary file, returning a NULL in the process.

Another possible reason tmpfile() might fail is if the root directory is full. MS-DOS allows only a limited amount of file entries in the root directory depending on the disk format; therefore, if the root is full, you must delete some files before you use tmpfile().