Windows File I/O vs. C Run-time File I/O

ID: Q11988

The information in this article applies to:

Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1

SUMMARY

The following functions are provided by the Microsoft C Run-time Library (CRT) and the Windows API to create a file:


   Return Type    API or Function   Category
   --------------------------------------------
   HFILE          OpenFile          Windows API
   HFILE          _lopen/_lcreat    Windows API
   int            _open/_creat      CRT
   FILE *         fopen             CRT

These return types (HFILE, int, and FILE *) are not compatible, so they can not be used in a function which is expecting the other type. The HFILEs are handles to operating system files (MS-DOS file handles), the ints are CRT file handles, and the FILE *s are pointers to structures which represent a CRT stream.

For files opened with OpenFile(), _lopen, and _lcreat, the common file manipuluation routines that you should use are:

_lclose
_llseek
_lread
_lwrite

For files opened with _open() and _creat(), the common file manipulation routines that you should use are:

_close
_lseek
_read
_write

For files opened with fopen, the common file manipulation routines that you should use are:

fclose
fseek
fread
fwrite

For other input and output functions, please check the documentation for information on whether they are intended for use with MS-DOS handles (HFILE), streams (FILE *), or low-level I/O (int).

MORE INFORMATION

An application should use the OpenFile() API any time an MS-DOS file handle is required.

The open functions do not necessarily open a file in binary raw mode; the application is required to set the binary attribute explicitly. The OpenFile() function automatically performs this step.

If the filename parameter specifies only a filename and extension, the open functions search for a matching file only in the current directory.

In Windows, the OpenFile() API creates an MS-DOS file handle through which an application can access Windows-specific files. OpenFile() initially opens the file in binary raw mode by performing an MS-DOS Interrupt 21h Function 3Dh. If the lpFileName parameter specifies only a filename and an extension, OpenFile() searches for a matching file in the following directories:

The current directory.

The Windows directory. The GetWindowsDirectory() API returns the path to this directory.

The Windows system directory . The GetSystemDirectory() API returns the path to this directory.

The directories listed in the PATH environment variable.

Additional query words: 3.00 3.10

Keywords : kb16bitonly
Version : WINDOWS:3.0,3.1
Platform : WINDOWS
Issue type :