보안 버퍼오버플로우를 잘 모르겠습니다(소스)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#pragma warning(disable:4996)
 
void a(char *out, FILE *fp){
  int r,i = 0;
  char buf[1];
 
  while ((r = fread(buf, 1, 1, fp)) > 0)
    out[i++] = buf[0];
 
  out[i] = 1/(400-i);
}
 
void b(FILE *fp, char *argv){
  char buf[256];
  a(buf, fp);
  printf("[FILE: %s]\n%s\n", argv, buf);
  *argv = NULL;
}
 
void c(){
  printf("You win!\n");
}
 
int main(int argc, char *argv[]){
  FILE *pFile;
 
  if (argc != 2){
    fprintf(stderr, "Usage: TxtReader.exe filepath\n");
    exit(1);
  }else{
    pFile = fopen(argv[1], "rb");
 
    if (pFile == NULL){
      fprintf(stderr, "Error: Invalid file path\n");
      exit(1);
    }
  }
 
  b(pFile, argv[1]);
  fclose(pFile);
 
  return 0;
}