程序代码：

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
struct
{
    FILE *pfile;
    char fname[20];
}file={NULL,"information"};
void list_file(void);
int main(void)
{
    int len;
    int age=0;
    char ch='y';
    char name[20];
    if(!(file.pfile=fopen(file.fname,"wb")))
    {
        printf("\nCannnot write file\n");
        exit(1);
    }
    do
    {
        fflush(stdin);
        printf("Please input name(letter<20)\n");
        gets(name);
        printf("Please input age\n");
        scanf("%d",&age);
        len=strlen(name);
        fwrite(&len,sizeof len,1,file.pfile);
        fwrite(name,len,1,file.pfile);
        fwrite(&age,sizeof(age),1,file.pfile);
        printf("\nDo you want to enter another(y/n)\n");
        scanf(" %c",&ch);
    }
    while(tolower(ch)=='y');
    fclose(file.pfile);
    list_file();
    system("pause");
    return 0;
}
void list_file(void)
{
    char name[20];
    int age;
    int len;
    if(!(file.pfile=fopen(file.fname,"rb")))
    {
        printf("\nCannot read file\n");
        exit(1);
    }
    while(fread(&len,sizeof len,1,file.pfile))
    {
   

        if(len<=20)
        {
            fread(name,len,1,file.pfile);----------------------用strlen（name）返回 3（假设输入qwe）；
            printf("%-20s",name);------------------------------再次用strlen（name）返回 31；
            fread(&age,sizeof age,1,file.pfile);
            printf(" %d\n",age);
        }
        else
            {
                printf("Name too long,cannot show it\n");
                system("pause");
            }
                                                              

    }
    fclose(file.pfile);
}