c语言中ftell函数是什么

#include <stdio.h>

#include <stdlib.h>//fseek函数调用

int main()

{

    long position;

    char list[100];

    /*    rb+ 读写打开一个二进制文件，允许读数据。*/

    FILE * fp = fopen("a.txt", "rb+");

    if (fp == NULL) {

        printf("file error\n");

        exit(1);

    }

    fread(list,sizeof(char),100,stream);

    //get position after read

    position=ftell(stream);

    printf("Position after trying to read 100 bytes:%ld\n",position);

    fclose(stream);

    stream=NULL;

    return 0;

}