The Linux Programming Interface

File I/O: Further Details 101

Listing 5-2: Performing scatter input with readv()

–––––––––––––––––––––––––––––––––––––––––––––––––––––––––– fileio/t_readv.c
#include <sys/stat.h>
#include <sys/uio.h>
#include <fcntl.h>
#include "tlpi_hdr.h"

int
main(int argc, char argv[])
{
int fd;
struct iovec iov[3];
struct stat myStruct; / First buffer /
int x; / Second buffer /
#define STR_SIZE 100
char str[STR_SIZE]; / Third buffer */
ssize_t numRead, totRequired;

if (argc != 2 || strcmp(argv[1], "--help") == 0)
usageErr("%s file\n", argv[0]);

fd = open(argv[1], O_RDONLY);
if (fd == -1)
errExit("open");

totRequired = 0;

iov[0].iov_base = &myStruct;
iov[0].iov_len = sizeof(struct stat);
totRequired += iov[0].iov_len;

iov[1].iov_base = &x;
iov[1].iov_len = sizeof(x);
totRequired += iov[1].iov_len;

iov[2].iov_base = str;
iov[2].iov_len = STR_SIZE;
totRequired += iov[2].iov_len;

numRead = readv(fd, iov, 3);
if (numRead == -1)
errExit("readv");

if (numRead < totRequired)
printf("Read fewer bytes than requested\n");

printf("total bytes requested: %ld; bytes read: %ld\n",
(long) totRequired, (long) numRead);
exit(EXIT_SUCCESS);
}
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––– fileio/t_readv.c