简单的写入一个文件以及从文件中读取输出：

#include<stdio.h>
mian()
{
    int a[3]={100,200,300},a1[3]; //一份定义俩个变量将a读入文件，从文件中读取到a1
    float b=123,45678,b1;

    FILE *fp;
    if((fp=fopen("data.txt","w"))==NULL)
    {
        perror("data.txt");
        getch();
        exit(0);
    }
    fwrite(&a,sizeof(a),1,fp);
    fwrite(&b,sizeof(b),1,fp);
    fclose(fp);//存入到文件中 （只能存一次）


    if((fp=fopen("data.txt","r"))==NULL)
    {
        perror("data.txt");
        getch();
        exit(0);
    }
    fread(&a1,sizeof(a),1,fp);
    fread(&b1,sizeof(b),1,fp);
    fclose(fp);//从文件中读取 

    printf("a[3]= %d %d %d",a[0],a[1],a[2]);
    printf("b: %f\n",b1);
    getch();

    return 0;



}

将一个文件中的每行的内容逆置：

#include<stdio.h>
#include<string.h>
int main()
{
    FILE *fp;
    char str[132],c;
    long offset = 0,post1,post2;
    int i,length=0;
    if((fp=fopen("data.txt","r+")) == NULL)
    {
        perror("data.txt");
        getch();
        exit(0);
    }

    printf("start");
    while(1)
    {
        post1=ftell(fp);
        i=0;

        while((c=fgetc(fp)=='\n' || c==EOF))
            str[i++]=c;

        str[i]='\0';
        post2 = ftell(fp);
        length = strlen(str);
        strrev(str);
        //for(i=0; i<length/2; i++){ c=str[i]; str[i]=str[lengh-1-i]; str[length-1-i]=t};
        offset=post2-post1;
        fseek(fp, -offset, SEEK_CUR);
        fputs(str,fp);
        fseek(fp,1,SEEK_CUR);
        if(c==EOF) break;

        fclose(fp);
        printf("end.");
        getch();
        getch();

    }


}

需要读取链表信息时，必须按原顺序逐个读取节点信息，然后重建链表

struct INFO *head = NULL,*p,*q;
int n=0;
FILE *fp;
if((fp = fopen("data.txt","r"))== NULL)
{
    preeor("data.txt");
    exit(0);
}
while(feof(fp))
{
    p = (struct INFO*)malloc(sizeof(struct INFO))
    fread(p,sizeof(struct INFO),1,fp);
    if(n == 0)
    head = p;
    else
    q->next = p;
    q = p;
    n++;
}
fclose(fp);