按数据块读写文件

函数fread（）和fwrite（）用于一次读取一组数据，即按数据块读写文件。

fread（）函数

函数的原型：

unsigned int fread(void *buffer, unsigned int size, unsigned int countn, FILE *fp);

功能：fread（）函数的功能是从fp所指的文件中读取数据块并存储到buffer指向的内存中。

参数的用途：buffer是待读入数据块的起始地址。size是每个数据块的大小（待读入的每个数据块的字节数）。count是最多允许读取的数据块个数（每个数据块size个字节）。

返回值类型：函数返回的是实际写入的数据块个数

块数据的读写使我们不再局限于一个只读取一个字符、一个单词或一行字符串，它允许用户指定想要读写的内存放大小，最小为1个字节，最大为整个文件。

此实例的程序的前提是在D盘中已经有了一个名为score.txt文件

#include<stdio.h>
#include<stdlib.h>
#define N 30
typedef struct date
{
    int year;
    int month;
    int day;
}DATE;
typedef  struct  student
{
    long studentID;
    char studentName[10];
    char studentSex;
    DATE birthday;
    int score[4];
    float aver;
}STUDENT;
void InputScore(STUDENT stu[],int n,int m);
void AverScore(STUDENT stu[], int n, int m);
void WritetoFile(STUDENT stu[],int n);
void PrintScore(STUDENT stu[], int n, int m);
int ReadfromFile(STUDENT stu[]);
int main()
{
    STUDENT stu[N];
    int n, m = 4;
    printf("How many student?\n");
    scanf("%d",&n);
    InputScore(stu,n,m);
    AverScore(stu,n,m);
    WritetoFile(stu,n);
    n = ReadfromFile(stu);
    PrintScore(stu, n, m);
    return 0;
}
void InputScore(STUDENT stu[],int n,int m)
{
    int i,j;
    for(i = 0; i < n; i++)
    {
        printf("Input record %d:\n",i+1);
        scanf("%ld",&stu[i].studentID);
        scanf("%s",stu[i].studentName);
        scanf(" %c",&stu[i].studentSex);
        scanf("%d",&stu[i].birthday.year);
        scanf("%d",&stu[i].birthday.month);
        scanf("%d",&stu[i].birthday.day);
        for(j = 0; j < m; j++)
        {
            scanf("%d", &stu[i].score[j]);
        }
    }
}
void AverScore(STUDENT  stu[], int n, int m)
{
    int i, j, sum;
    for(i = 0; i < n; i++)
    {
        sum = 0;
        for(j = 0; j < m; j++)
        {
            sum = sum + stu[i].score[j];
        }
        stu[i].aver = (float)sum / m;

    }
}
void WritetoFile(STUDENT stu[],int n)
{
    FILE *fp;
    int i,j;
    if((fp = fopen("D:\\student.txt","w")) == NULL)
    {
        printf("Failure to open score.txt!\n");
        exit(0);
    }
    fwrite(stu, sizeof(STUDENT), n, fp);
    fclose(fp);
}
int ReadfromFile(STUDENT stu[])
{
    FILE *fp;
    int i,j;
    if((fp = fopen("D:\\student.txt","r")) == NULL)
    {
        printf("Failure to open score.txt!\n");
        exit(0);
    }
    for(i = 0; !feof(fp); i++)
    {
        fread(&stu[i],sizeof(STUDENT),1,fp);
    }
    fclose(fp);
    printf("Total student is %d.\n",i-1);

    return i - 1;
}
void PrintScore(STUDENT stu[], int n, int m)
{
    int i,j;
    for( i = 0; i < n; i++)
    {
        printf("%10ld%8s%3c%6d/%02d/%02d",stu[i].studentID,stu[i].studentName,stu[i].studentSex,
               stu[i].birthday.year,stu[i].birthday.month,stu[i].birthday.day);
        for(j = 0; j < m; j++)
        {
            printf("%4d",stu[i].score[j]);
        }
        printf("%6.1f\n",stu[i].aver);
    }

}

/将输入的数据写入名为student.txt的文件中/

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