file_align.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

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

#define MAX_BUFF_SIZE 100

static off_t fsize(char *path);

/* usage:
 *   ./main orgfName modfName Padded
 */
int main(int argc, char *argv[])
{
    assert(argc == 4 && "./main orgfName modfName Padded");

    char *org = argv[1];
    char *mod = argv[2];
    int pad = atoi(argv[3]);

    printf("orginal file size = %ld\n", fsize(org));

    FILE *fd0 = fopen(org, "r");
    FILE *fd1 = fopen(mod, "w+");

    char rbuf[MAX_BUFF_SIZE];
    int suffix;

    char *wbuf = (char *) malloc(sizeof(char) * pad);

    while (fgets(rbuf, sizeof(rbuf), fd0)) {
        memset(wbuf, '\0', pad);

        if ((suffix = (pad - strlen(rbuf))) != 0)
            strncpy(wbuf, rbuf,strlen(rbuf));

        fwrite(wbuf, pad, 1, fd1);
    }

    fclose(fd0);
    fclose(fd1);

    return 0;
}

static off_t fsize(char *path)
{
    struct stat st;
    stat(path, &st);
    return st.st_size;
}