read/write/lseek example

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>

#define NSTRING 5
#define STRSIZE 3

char *string[] = { "aaa", "bbb", "ccc", "ddd", "eee" };

int main(int argc, char **argv) {
    int n, fd;
    char *fname;
    char buf[STRSIZE], answer[8], template[32];
    strcpy(template, "/tmp/seekerXXXXXX");
    fname = mktemp(template);

    fd = open(fname, O_RDWR | O_CREAT | O_TRUNC, 0666);

   printf ("debug) file name is %s\n", fname);

    for (n = 0 ; n < NSTRING ; n++) {
        write(fd, string[n], STRSIZE);
    }

    for ( ; ; ) {
        write(1, "which string ? ", 15);
        n = read(0, answer, sizeof(answer));
        answer[n-1] = '\0';
        n = atoi(answer);

        printf ("debug) n is %d\n", n);
        printf ("debug) fd is %d\n", fd);
        if (n == 0) {
            close(fd);
            return -1;
        }


        if (n < 0 || n > NSTRING) {
            write (2, "out of range\n", 13);
            continue;
        }

        lseek (fd, (n-1) *STRSIZE, SEEK_SET);
        read (fd, buf, STRSIZE);
        write(1, "String", 7);
        write(1, answer, strlen(answer));
        write(1, " = ", 3);
        write(1, buf, STRSIZE);
        write(1, "\n\n", 2);
    }
    return 0;
}

 read/write/lseek system call을 사용한 예제이다. 

fd의 0은 stdin, 1은 stdout, 2는 stderr를 의미. 예약된 번호이다.