[C++知识库]IO、进程、线程

//守护进程
int main(){
	
	int res=fork();//创建子进程
		int  i=0;
		
		if(res >)){
		exit(0);//关闭父进程
		}
		setsid();//创建新会话
		
		chdir("/");//切换当前工作目录到根目录
		
		umask(0);//重新设置文件权限掩码
		
		//for()
		//close();//关闭不需要的文件描述符号
		close(0);
		close(1);
		colse(3);
}

#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
int Create_Daemon()
{
    int pid;
    //屏蔽一些控制终端信号    
    signal(SIGTTOU,SIG_IGN);   
    signal(SIGTTIN,SIG_IGN);   
    signal(SIGTSTP,SIG_IGN);   
    signal(SIGHUP ,SIG_IGN); 
    //设置文件掩码
    umask(0);
    //调用fork函数，父进程退出
    pid = fork();
    if(pid < 0 )
    {
        printf("error fork");
        return -1;
    }
    else if(pid > 0)
    {//father
        exit(0);
    }
    //设置新会话
    setsid();
    //处理SIGCHlD信号
    signal(SIGCHLD,SIG_IGN);

    //禁止进程重新打开控制终端
    if(pid = fork())
    {//father
        exit(0);
    }
    else if(pid <0)
    {
        perror("fork");
        exit(-1);
    }

    //关闭打开的文件描述符
    close(0);close(1);close(2);

    //改变当前的工作目录
    chdir("/");

    return 0;
}

int main()
{
    Create_Daemon();
    while(1);
    return 0;
}
//线程同步
#include<stdio.h>
#include<pthread.h>
#include<string.h>
#include<semaphore.h>
#include<stdlib.h>

int ThreadVal=0;
sem_t sem1,sem2;
void *fun1(void *arg){
	while(1){
		sem_wait(&sem1);//P  1  0
		sleep(1);
		if(ThreadVal<0){
			sem_post(&sem2);//V
			pthread_exit(NULL);		
		}
		ThreadVal++;
		printf("+++++thread1 ThreadVal=%d\n",ThreadVal);
		sem_post(&sem2);//0  1 	
	}
}
void *fun2(void *arg){
	while(1){
		sem_wait(&sem2);//1  0
		sleep(1);
		if(ThreadVal<0){
			sem_post(&sem1);
			pthread_exit(NULL);
		}
		ThreadVal-=2;
		printf("-----thread2 ThreadVal=%d\n",ThreadVal);
		sem_post(&sem1);//0  1
	}
	
}

int main(int argc,char *argv[]){
	if(argc<2){
		return -1;
	}
	ThreadVal=atoi(argv[1]);
	//初始化信号量
	pthread_t thread1,thread2;
	int ret=0;
	
	ret=sem_init(&sem1,0,1);
	
	ret=sem_init(&sem2,0,0);
	
	ret=pthread_create(&thread1,NULL,fun1,NULL);
	
	ret=pthread_create(&thread2,NULL,fun2,NULL);

	pthread_join(thread1,NULL);
	pthread_join(thread2,NULL);
	return 0;

}
//进程创建（fork）

int main(){
	pid_t pid;
	
	pid=fork();
	
	if(pid==0){
		printf("i am  a child\n");
	}else{
		sleep(1);
		printf("i am father\n");
	}
	return 0;
}


//互斥锁

#include<stdio.h>
#include<pthread.h>
//互斥锁
int a=0;
int b=0;
pthread_mutex_t mutex;//声明互斥锁
void *fun1(void *arg){
	while(1){
		pthread_mutex_lock(&mutex);
		a++;
		b++;
		if(a!=b){
			printf("%d!=%d\n",a,b);
			a=b=0;	
		}else{
			printf("%d==%d\n",a,b);
		}
		pthread_mutex_unlock(&mutex);
	}

}
void *fun2(void *arg){
	while(1){
		pthread_mutex_lock(&mutex);
		a++;
		b++;
		if(a!=b){
			printf("%d!=%d",a,b);
			a=b=0;	
		}
		pthread_mutex_unlock(&mutex);
	}

}
int main(){
	

	//声明两个线程
	pthread_t thread1,thread2;
	//初始化锁
	pthread_mutex_init(&mutex,NULL);
	
	//创建线程
	pthread_create(&thread1,NULL,fun1,NULL);
	pthread_create(&thread2,NULL,fun2,NULL);
	
	pthread_join(thread1,NULL);
	pthread_join(thread2,NULL);
	pthread_mutex_destroy(&mutex);
	
	return 0;
}



//统计文件行数
#include <stdio.h>
#include<string.h>
int main()
{	
	FILE *f;
	
	f=fopen("file1.txt","r");
	
    char buf1[20]="";
	int count=0;
	
	while(fgets(buf1,20,f)){
		if(buf1[strlen(buf1)-1]=='\n'){
			count++;		
		}
	}
	printf("%d\n",count);
	close(f);
    return 0;
}

//管道
reader.c     从argv[1]所指定的文件中读取内容，依次写到管道/home/linux/myfifo中
writer.c     从管道/home/linux/myfifo中读取内容，写到argv[1]所指定的文件中并保存

代码中可省略头文件，/home/linux/myfifo无需创建
#include<stdio.h>

int main(int argc,char *argv[]){

	int fd,fd_scr;
	char buf[32];
	int bytes;
	if(argc<2){
		return -1;	
	}
	fd=open("/home/linux/myfifo",O_WRONLY);
	if(fd<0){
		return -1;
	}
	fd_src=open(argv[1],O_RDONLY);
	if(fd_src<0){
		return -1;
	}
	while((bytes=read(fd_src,buf,32))>0){
		write(fd,buf,bytes);	
	}
	close(fd);
	close(fd_src);
	
	return 0;
}

int main(int argc,char *argv[]){

	int fd,fd_dest;
	char buf[32];
	int bytes;
	if(argc<2){
		return -1;	
	}
	fd=open("/home/linux/myfifo",O_RDONLY);
	if(fd<0){
		return -1;
	}
	fd_dest=open(argv[1],O_WRONLY|O_CREAT|O_TRUNC,0666);
	if(fd_src<0){
		return -1;
	}
	while((bytes=read(fd_src,buf,32))>0){
		write(fd_dest,buf,bytes);	
	}
	close(fd);
	close(fd_dest);
	
	return 0;
}