system-call-read-from-disk.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>

void readfile(int fd);

int main(int argc, char** argv) {
    if (argc != 2) {
        printf("Usage: %s <filename>\n", argv[0]);
        return -1;
    }
    int fd = open(argv[1], O_RDONLY);
    if (fd == -1) {
        printf("Unable to open file! Is %s a valid name?", argv[1]);
        return -1;
    }
    readfile(fd);
    close(fd);
    return 0;
}

void readfile(int fd) {
    int buffer_size = 256;
    char* buffer = malloc(buffer_size);
    while (1) {
        memset(buffer, 0, buffer_size);
        int bytes_read = read(fd, buffer, buffer_size - 1);
        if (bytes_read == 0) {
            break;
        }
        printf("%s", buffer);
    }
    printf("\nEnd of file.\n");
    free(buffer);
}