Change the file-permission settings.
int _chmod( const char *filename, int pmode );
int _wchmod( const wchar_t *filename, int pmode );
| Routine | Required Header | Optional Headers | Compatibility |
| _chmod | <io.h> | <sys/types.h>, <sys/stat.h>, <errno.h> | Win 95, Win NT |
| _wchmod | <io.h> or <wchar.h> | <sys/types.h>, <sys/stat.h>, <errno.h> | Win NT |
For additional compatibility information, see Compatibility in the Introduction.
Libraries
| LIBC.LIB | Single thread static library, retail version |
| LIBCMT.LIB | Multithread static library, retail version |
| MSVCRT.LIB | Import library for MSVCRT.DLL, retail version |
Return Value
Each of these functions returns 0 if the permission setting is successfully changed. A return value of –1 indicates that the specified file could not be found, in which case errno is set to ENOENT.
Parameters
filename
Name of existing file
pmode
Permission setting for file
Remarks
The _chmod function changes the permission setting of the file specified by filename. The permission setting controls read and write access to the file. The integer expression pmode contains one or both of the following manifest constants, defined in SYS\STAT.H:
_S_IWRITE
Writing permitted
_S_IREAD
Reading permitted
_S_IREAD | _S_IWRITE
Reading and writing permitted
Any other values for pmode are ignored. When both constants are given, they are joined with the bitwise-OR operator ( | ). If write permission is not given, the file is read-only. Note that all files are always readable; it is not possible to give write-only permission. Thus the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.
_wchmod is a wide-character version of _chmod; the filename argument to _wchmod is a wide-character string. _wchmod and _chmod behave identically otherwise.
Generic-Text Routine Mappings
| TCHAR.H Routine | _UNICODE & _MBCS Not Defined | _MBCS Defined | _UNICODE Defined |
| _tchmod | _chmod | _chmod | _wchmod |
Example
/* CHMOD.C: This program uses _chmod to
* change the mode of a file to read-only.
* It then attempts to modify the file.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#include <stdio.h>
#include <stdlib.h>
void main( void )
{
/* Make file read-only: */
if( _chmod( "CHMOD.C", _S_IREAD ) == -1 )
perror( "File not found\n" );
else
printf( "Mode changed to read-only\n" );
system( "echo /* End of file */ >> CHMOD.C" );
/* Change back to read/write: */
if( _chmod( "CHMOD.C", _S_IWRITE ) == -1 )
perror( "File not found\n" );
else
printf( "Mode changed to read/write\n" );
system( "echo /* End of file */ >> CHMOD.C" );
}
Output
Mode changed to read-only
Access is denied
Mode changed to read/write