read

Remonter à Io.h - Index

Header File

io.h

Category

Input/output Routines

Prototype

int read(int handle, void *buf, unsigned len);

Description

Reads from file.

read attempts to read len bytes from the file associated with handle into the buffer pointed to by buf.

For a file opened in text mode, read removes carriage returns and reports end-of-file when it reaches a Ctrl-Z.

The file handle handle is obtained from a creat, open, dup, or dup2 call.

On disk files, read begins reading at the current file pointer. When the reading is complete, it increments the file pointer by the number of bytes read. On devices, the bytes are read directly from the device.

The maximum number of bytes that read can read is UINT_MAX -1, because UINT_MAX is the same as -1, the error return indicator. UINT_MAX is defined in limits.h.

Return Value

On successful completion, read returns an integer indicating the number of bytes placed in the buffer. If the file was opened in text mode, read does not count carriage returns or Ctrl-Z characters in the number of bytes read.

On end-of-file, read returns 0. On error, read returns -1 and sets the global variable errno to one of the following values:

EACCES	Permission denied
EBADF	Bad file number

Example

 #include <stdio.h>
 #include <io.h>
 #include <alloc.h>
 #include <fcntl.h>
 #include <process.h>
 #include <sys\stat.h>
 int main(void)
 {
    void *buf;
    int handle, bytes;
    buf = malloc(10);
 /*
 Looks for a file in the current directory named TEST.$$$ and attempts to read 10 bytes from it. To use this example you should create the file TEST.$$$.
  */
    if ((handle =
       open("TEST.$$$", O_RDONLY | O_BINARY, S_IWRITE | S_IREAD)) == -1)
    {
       printf("Error Opening File\n");
       exit(1);
    }
    if ((bytes = read(handle, buf, 10)) == -1) {
       printf("Read Failed.\n");
       exit(1);
    }
    else {
       printf("Read: %d bytes read.\n", bytes);
    }
    return 0;
 }

Portability

POSIX	Win32	ANSI C	ANSI C++
+	+