#include <stdio.h>
#include <stdlib.h>
#define _STDC_WANT_LIB_EXT1_

int main ()
{
    long num1=234567L;
    long num2=345123L;
    long num3=789234L;
    long num4=0L;
    long num5=0L;
    long num6=0L;
    float fnum=0.0f;
    int ival[6]={0};
    FILE *pfile=NULL;
    char *filename ="myfile.txt";

    if(fopen_s(&pfile,filename,"w"))
    {
        printf("Failed to open the file.\n");
        exit (1);
    }
    setbuf(pfile,NULL);
    fprintf_s(pfile,"%6ld%6ld%6ld",num1,num2,num3);
    fclose(pfile);
    if(fopen_s(&pfile,filename,"r"))
    {
        printf("Failed to open the file");
    }
        setbuf(pfile,NULL);
        fscanf(pfile,"%6l%6l%6l",&num4,&num5,&num6);
    printf("%6ld%6ld%6ld",num4,num5,num6);
   
    fclose (pfile);
    putchar (10);
    system ("pause");
    return 0;
}

运行结果如下：
通过单步调试，发现在第一个fprintf函数那里出错。下面是我从百度下载的代码，进行了简单的修改：
#include <stdio.h>
#include <stdlib.h>
int main()
{
    FILE *fp;
    int i=617;
    char rec[100]={'\0'};
    char* s = "that is a good new";
    fp = fopen("D:\\text.dat","w");
    fputs("total",fp);
    fputs(":",fp);
    fprintf(fp,"%d\n",i);
    fprintf(fp,"%s",s);
    rewind(fp);
    fscanf(fp,"%s",rec);
    printf("%s",rec);
    fclose(fp);
   
    system ("pause");
    return 0;
}
编译无错误，但是运行结果不对,请见图片：




求大神解释这是怎么回事。。。

谢谢您的提醒，我一定会加倍努力地