write

Remonter à Io.h - Index

Header File

io.h

Category

Input/output Routines

Prototype

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

Description

Writes to a file.

write writes a buffer of data to the file or device named by the given handle. handle is a file handle obtained from a creat, open, dup, or dup2 call.

This function attempts to write len bytes from the buffer pointed to by buf to the file associated with handle. Except when write is used to write to a text file, the number of bytes written to the file will be no more than the number requested. The maximum number of bytes that write can write is UINT_MAX -1, because UINT_MAX is the same as -1, which is the error return indicator for write. On text files, when write sees a linefeed (LF) character, it outputs a CR/LF pair. UINT_MAX is defined in limits.h.

If the number of bytes actually written is less than that requested, the condition should be considered an error and probably indicates a full disk. For disks or disk files, writing always proceeds from the current file pointer. For devices, bytes are sent directly to the device. For files opened with the O_APPEND option, the file pointer is positioned to EOF by write before writing the data.

Return Value

write returns the number of bytes written. A write to a text file does not count generated carriage returns. In case of error, write 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 <stdlib.h>
 #include <fcntl.h>
 #include <sys\stat.h>
 #include <io.h>
 #include <string.h>
 int main(void)
 {
    int handle;
    char string[40];
    int length, res;
 /*
 Create a file named "TEST.$$$" in the current directory and write a string to it.  If "TEST.$$$" already exists, it will be overwritten.
  */
    if ((handle = open("TEST.$$$", O_WRONLY | O_CREAT | O_TRUNC,
                          S_IREAD | S_IWRITE)) == -1)
    {
       printf("Error opening file.\n");
       exit(1);
    }
    strcpy(string, "Hello, world!\n");
    length = strlen(string);
    if ((res = write(handle, string, length)) != length)
    {
       printf("Error writing to the file.\n");
       exit(1);
    }
    printf("Wrote %d bytes to the file.\n", res);
    close(handle);
    return 0;
 }

Portability

POSIX	Win32	ANSI C	ANSI C++
+	+