read Function

The read function is used to read data from a file (identified by a handle), without formatting, type conversion, or buffering.

Handle

Selector (file descriptor) of an open file.

Buffer

The address where the data read is to be stored.

Length

The number of bytes to be read.

int

Number of bytes read.

errno

Iff the read fails, the global variable errno is set to one of:

EBADF

Handle not open

#include <stdio.h>
#include <io.h> 
#include <fcntl.h>
#include <errno.h>

int main () {
  int Account_Master;
  char Buffer [100]; 
  int Maximum; 
  int Actual;
  /* Other declarations */
  Maximum = 100;
  Account_Master = open ("accounts.dat", O_RDONLY);
  if (Account_Master >0) {
    printf ("Open succeeded.\n");
  } else {
    printf ("Open failed.\n")
    switch (errno) {
      case EACCES:  printf ("Permission denied.\n"); break;
      case EINVACC: printf ("Invalid access mode.\n"); break;
      case EMFILE:  printf ("No file handle available.\n"); break;
      case ENOENT:  printf ("File or path not found.\n"); break;
      default:      printf ("Unknown error.\n"); break;
    }
  /* File processing */
  Actual = 1;
  while (Actual > 0)
    Actual = read (Account_Master, Buffer, Maximum); 
    if (Actual < Maximum) { 
      printf ("An incomplete record was read.\n")
    }
    /* Record processing */
  }
  
  if (close (Account_Master) == 0) {
    printf ("Close succeeded.\n");
  } else {
    printf ("Close failed.\n")
    switch (errno) {
      case EBADF:  printf ("File not open.\n"); break;
      default:     printf ("Unknown error.\n"); break;
    }
  }
  return 0;
}