lseek
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h> // printf()
#include <stdlib.h> // exit()
int main() {
int fd = open("words.txt", O_RDONLY);
if (fd < 0) exit(1);
char word[4];
off_t new_pos = lseek(fd, 4, SEEK_SET);
read(fd, word, 3);
word[4] = 0;
printf("Word @ pos %d: %s\n", new_pos, word);
new_pos = lseek(fd, 1, SEEK_CUR); // Skip new line characters
read(fd, word, 3);
printf("Word @ pos %d: %s\n", new_pos, word);
close(fd);
}
If successful, lseek returns the new offset from the beginning of the file in bytes.
If not successful, lseek returns -1.
fseek
#include <stdio.h>
#include <stdlib.h> // exit()
int main() {
FILE *f = fopen("words.txt", "r");
if (!f) exit(1);
char word[4];
word[4] = 0; // Words contain three characters.
if (fseek(f, 4, SEEK_SET)) exit(2);
//
// We want to read 3 chars:
//
size_t size = sizeof(char);
size_t nmemb = 3 ;
size_t nof_items_read = fread(word, size, nmemb, f);
if (nof_items_read != 3) exit(3);
printf("Word: %s\n", word);
//
// Advance file position indicator by one character:
//
if (fseek(f, 1, SEEK_CUR)) exit(4);
//
// Read another word
//
nof_items_read = fread(word, size, nmemb, f);
if (nof_items_read != 3) exit(3);
printf("Word: %s\n", word);
fclose(f);
}
If successful, fseek returns 0.