标准IO函数：fprintf和fscanf，fread和fwrite

1.使用分文件编译，实现注册登录界面，使用fgets，fscanf，fpritnf函数。

主函数

#include "log.h"
int main(int argc, const char *argv[])
{
	int key;
	while(1)
	{
		printf("**********1.注册**********\n");
		printf("**********2.登录**********\n");
		printf("**********3.退出**********\n");

		printf("\n请输入要执行的步骤：");
		scanf("%d",&key);
		getchar();

		switch(key)
		{
		case 1:regist();break;
		case 2:login();break;
		case 3:exit(EXIT_SUCCESS);break;
		}
	}
	
	return 0;
} 

 注册函数

#include"log.h"

int regist()
{
	user reg;
	printf("请输入注册账户:");
	fgets(reg.name,sizeof(reg.name),stdin);

	printf("请输入注册账户的密码:");
	fgets(reg.code,sizeof(reg.code),stdin);

	FILE *fp = fopen("./user.txt","w");
	if(fp==NULL)
	 {
		perror("fopen");
		 return -1;
	 }

	fprintf(fp,"%s%s",reg.name,reg.code);

	printf("注册成功\n");
	fclose(fp);

	return 0;

}

 登录函数：

#include"log.h"


int login()
{
	user reg,log;
	
	printf("请输入登录账户：");
    fgets(log.name,sizeof(log.name),stdin);

    printf("请输入登录密码：");
    fgets(log.code,sizeof(log.code),stdin);


	FILE *fp = fopen("./user.txt","r");
    if(fp==NULL)
    {
        perror("fopen");
        return -1;
    }

	fscanf(fp,"%s%s",reg.name,reg.code);
	reg.name[strlen(reg.name)+1]='\0';
	reg.name[strlen(reg.name)]='\n';
	reg.code[strlen(reg.code)]='\n';
	reg.code[strlen(reg.code)+1]='\0';

	printf("%s%s",reg.name,reg.code);

    if(strcmp(log.name,reg.name)==0&&
            strcmp(log.code,reg.code)==0)
    {
        printf("登录成功\n");
    }
    else
    {
        printf("登录失败，密码或账户名错误\n");
    }
	return 0;




}

另一种写法： 

int remove_line(char *str)
{
	int len = strlen(str);
    if(len>0 && str[len-1] =='\n')
	{
        str[len-1] ='\0';
    }
}
int login()
{
	user reg,log;

	printf("请输入登录账户：");
    fgets(log.name,sizeof(log.name),stdin);
	remove_line(log.name);
    printf("请输入登录密码：");
    fgets(log.code,sizeof(log.code),stdin);
	remove_line(log.code);

	FILE *fp = fopen("./user.txt","r");
    if(fp==NULL)
    {
        perror("fopen");
        return -1;
    }

	fscanf(fp,"%s%s",reg.name,reg.code);
	printf("%s%s",reg.name,reg.code);

    if(strcmp(log.name,reg.name)==0&&
            strcmp(log.code,reg.code)==0)
    {
        printf("登录成功\n");
    }
    else
    {
        printf("登录失败，密码或账户名错误\n");
    }
	return 0;

}

头文件：定义存储账户和密码的结构体 

#ifndef __LOG_H__
#define __LOG_H__

#include<myhead.h>

typedef struct
{
	char name[50];
	char code[50];
}user;

int login();
int regist();



#endif

2.使用fread和fwrite拷贝文件。

#include <myhead.h>
int main(int argc, const char *argv[])
{
	
	char arr[1024];
	FILE *fp1 = fopen("./1.txt","r");//只读方式打开文件1
    if(NULL==fp1)
    {
        perror("fp1");
        return -1;
    }
	fread(arr,sizeof(arr),1,fp1);

	
    FILE *fp2 = fopen("./2.txt","w");//只写清空方式打开文件2
    if(NULL==fp2)
    {
        perror("fp2");
        return -1;
    }

	fwrite(arr,sizeof(arr),1,fp2);

	fclose(fp1);
	fclose(fp2);

	char arr1[1024];
	fp2 = fopen("./2.txt","r");//只读方式打开文件2
    if(NULL==fp2)
    {
        perror("fp2");
        return -1;
	}
	fread(arr1,1,sizeof(arr1),fp2);
	printf("%s\n",arr1);
	fclose(fp2);
	return 0;
}