Header File 

io.h, fcntl.h 

Category 

Input/output Routines 

Prototype 

int open(const char *path, int access [, unsigned mode]); 

int _wopen(const wchar_t *path, int access [, unsigned mode]); 

Description 

Opens a file for reading or writing. 

open opens the file specified by path, then prepares it for reading and/or writing as determined by the value of access. 

To create a file in a particular mode, you can either assign to the global variable _fmode or call open with the O_CREAT and O_TRUNC options ORed with the translation mode desired.  

open("XMP",O_CREAT|O_TRUNC|O_BINARY,S_IREAD) 

creates a binary-mode, read-only file named XMP, truncating its length to 0 bytes if it already existed. 

For open, access is constructed by bitwise ORing flags from the following lists. Only one flag from the first list can be used (and one must be used); the remaining flags can be used in any logical combination. 

These symbolic constants are defined in fcntl.h. 

If neither O_BINARY nor O_TEXT is given, the file is opened in the translation mode set by the global variable _fmode. 

If the O_CREAT flag is used in constructing access, you need to supply the mode argument to open from the following symbolic constants defined in sys\stat.h.

Return Value 

On success, open returns a nonnegative integer (the file handle). The file pointer, which marks the current position in the file, is set to the beginning of the file.  

On error, open returns -1 and the global variable errno is set to one of the following values:

Example

#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
int main(void)
{
   int handle;
   char msg[] = "Hello world";
   if ((handle = open("TEST.$$$", O_CREAT | O_TEXT)) == -1)
   {
      perror("Error:");
      return 1;
   }
   write(handle, msg, strlen(msg));
   close(handle);
   return 0;
}

Portability