C 文件随机读写

#include <stdio.h>
#include <stdlib.h>

void eatline(){
    while(getchar()!='\n')
        continue;
}
//文件随机读写
int main(int argc, char * argv[])
{
    FILE *fp;
    int offset,tel;
    long in_stream;
    char ch,get;
    long pos;
    if((fp = fopen("E:/test/test.txt","r+b"))==NULL){
        fp = fopen("E:/test/test.txt","w+b");
        /*printf("Can't open this file.\n");
        exit (1);*/
    }
    
    while(1){
        puts("Usage: number alpha, first input with an alpha will stop.");
        int count = scanf("%d %c",&offset,&ch);
        eatline();
        if(count == 2){
            //定位文件指针
            fseek(fp,offset * sizeof(char),0);
            //取出当前指针指向的数据，并保存指针偏移量
            in_stream = fread(&get,sizeof(char),1,fp);
            printf("char=%c\n",get);
            //指针重新指向上一个索引处，并修改其中内容
            fseek(fp,-in_stream*sizeof(char),1);
            fwrite(&ch,sizeof(char),1,fp);
        }else{
            puts("Bye!");
            fclose(fp);
            return 0;
        }
    }
    
}