C ftell()函数

long int ftell(FILE *stream)

#include <stdio.h>
#include <conio.h>
void main (){
   FILE *fp;
   int length;
   clrscr();
   fp = fopen("file.txt", "r");
   fseek(fp, 0, SEEK_END);
   length = ftell(fp);
   fclose(fp);
   printf("Size of file: %d bytes", length);
   getch();
}

Size of file: 21 bytes