C-我的程序从文件读取后打印出奇怪的东西

Question

I am trying to make a program for an assignment to read ID3 tags. I don't have much code so far because I'm trying to learn how to work with the ID3 tags themselves. I made a little program which would read the first three letters and just print them back, just to see how the process of opening the file and closing it would work, etc.

This is my code:

#include <stdio.h>

int main(int argc, char *argv[]) {

  char buf[4];

  if (argc == 2) {
    FILE *mp3 = fopen(argv[1], "r");

    fread(buf, 3, 1, mp3);
    buf[3] = "\0";
    printf("%s\n", buf);
    fclose(mp3);
    char a = buf[0];
    char b = buf[1];
    char c = buf[2];
    printf("%x\t%x\t%x\n", a, b, c);
  }
  return 0;
}

It manages to print what is it supposed to (ID3) but then it makes some weird letters appear after the ID3 part. I added a part to print the hex values of those as well.

I am new to C and I find this very difficult to understand. Also, I don't quite understand the differences between all the different ways of making and managing a string. So I would greatly appreciate any help regarding this and how to make it better and explain to me why etc.

Answer 1

The part where you assign "\\0" to buf[3] is wrong. You should use single quotes:

buf[3] = '\0';

The reason is that double quotes means a string literal (which is a null terminated char array) and not a char variable.