为什么不用ww +覆盖我的数据？

Question

我在C中编写了一个小程序，用于在二进制文件中创建学生列表。我调用函数fsearch()（下面）来搜索指定的学生并更改他的数据，但似乎没有修改数据。

// the file is opened in mode "wb+"
int fsearch(FILE *f)
{
    student s;
    float matsearch;
    printf("enter the matricule you want to find ");
    scanf("%f",&matsearch);
    rewind(f); // starting the search from the beginning
    while(fread(&s,sizeof(student),1,f)==1 && s.mat!=matsearch);
    if(s.mat==matsearch)
    {
        printf("we found what searched for\n");
        printf("name: %s\n",s.fname);
        printf("last name: %s\n",s.lname);
        printf("matricule: %.f\n",s.mat);
        fseek(f,-sizeof(student),SEEK_CUR);     
        student a;
        scanf("%s",&(a.fname));
        scanf("%s",&(a.lname));
        scanf("%d",&(a.mat));
        if(fwrite(&a,sizeof(student),1,f)==1)
        {
             printf("successfully wrote");  // this message does get printed
        }
        return(1); // successfully found
    }

    printf("we didn't find what you searched for\n");
    return(0);
}