UC编程04-io读写write/read系统函数的使用

////myuc.h

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<fcntl.h>
#include<string.h>
#include<sys/types.h>
#include<sys/mman.h>
#include<sys/stat.h>

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
//#include<sys/types.h>
//#include<sys/stat.h>
#include<string.h>
#include<fcntl.h>
int main(){
	//系统会减去other组的写权限
	int fd=open("open4.txt",O_RDWR|O_CREAT|O_TRUNC,0777);
	if(fd==-1)
		perror("open"),exit(-1);//连接两个语句
	char buf[100]={};
	strcpy(buf,"mybuff1\n");
	write(fd,buf,strlen(buf));
	printf("openok,fd=%d\n",fd);
	close(fd);
	int fd2=open("open4.txt",O_RDONLY);
	if(fd2==-1) perror("open read"),exit(-1);
	memset(buf,0,sizeof(buf));
	int readcount=read(fd,buf,sizeof(buf));
	printf("fd2:%d,readed(%d):%s\n",fd2,readcount,buf);
	close(fd2);
	fd2=open("a.out",O_RDONLY);
	if(fd2==-1) perror("open src"),exit(-1);
	fd=open("a.out1",O_RDWR|O_CREAT|O_TRUNC,0777);
	if(fd==-1) perror("write dest"),exit(-1);
	//readcount=0;
	while(1){
		readcount=read(fd2,buf,sizeof(buf));
		if(readcount==0) break;
		else if(readcount==-1){
			perror("read src");break;
		}
   		write(fd,buf,readcount);
	}
	//while(readcount>0);
	close(fd);
	close(fd2);
	printf("文件复制成功！\n");
	
	return 0;
}

#include "myuc.h"
int main(){
	int fd=open("b.txt",O_RDWR);
	if(fd==-1) perror("open"),exit(-1);
	char ch;
	read(fd,&ch,1);
	printf("%c\n",ch);
	read(fd,&ch,1);
	printf("%c\n",ch);
	lseek(fd,7,SEEK_SET);
	read(fd,&ch,1);
	printf("%c\n",ch);
	lseek(fd,0,SEEK_SET);//回到开始
	write(fd,"1",1);//替换a
	lseek(fd,3,SEEK_SET);
	write(fd,"2",1);//替换d
	lseek(fd,-2,SEEK_END);//注意最后的\n,也是一个字节
	write(fd,"3",1);//替换到数第二个
	int len=lseek(fd,0,SEEK_END);//文件大小
	close(fd);
	return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
//#include<sys/types.h>
//#include<sys/stat.h>
#include<string.h>
#include<fcntl.h>
typedef struct EMP{
	int id;
	char name[100];
	double salary;
}emp;
int main(){
	int fd=open("write4.txt",O_CREAT|O_RDWR|O_APPEND,0777);
	if(fd==-1) perror("open"),exit(-1);
	printf("请输入编号，姓名，薪水：\n");
	emp em;
	scanf("%d%s%lf",&em.id,em.name,&em.salary);
	int res=write(fd,&em,sizeof(emp));
	if(res==-1) printf("失败\n");
	else printf("成功！\n");
	close(fd);
	fd=open("write4.txt",O_RDONLY);
	while(1)
	{
		res=read(fd,&em,sizeof(em));
		if(res==0) break;
		else if(res==-1) {
			perror("read");break;
		}
		printf("%d,%s,%g\n",em.id,em.name,em.salary);
	}
	close(fd);

	return 0;
}

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<fcntl.h>
void w1()//系统调用多，花时间多
{
	int fd=open("a.txt",O_CREAT|O_TRUNC,0777);
	if(fd==-1) perror("openwrite1"),exit(-1);
	int i;
	for(i=0;i<1000000;i++){
		write(fd,&i,4);
	}
}
void w2(){//系统调用少，省时间
	int fd=open("a.txt",O_RDWR|O_TRUNC);
	if(fd==-1) perror("openwrite2"),exit(-1);
	int arr[10000];
	int i;
	for(i=0;i<1000000;i++){
		arr[i%10000]=i;
		if(i%10000==9999) write(fd,arr,sizeof(arr));//10000个数字才写入一次
	}
	close(fd);
}
int main()
{
	//w1();
	w2();	
}