IO进程线程8.26

作业：创建3个进程，子进1程拷贝文件的前一半，子进程2拷贝后一半文件，父进程回收两个子进程资源

#include <myhead.h>

int get_len(const char *p1,const char *p2)
{
	
    int fd1 = open(p1,O_RDONLY);
	if(fd1==-1)
	{
		perror("open1");
		return -1;
	}
	
	int fd2 = open(p2,O_WRONLY|O_CREAT|O_TRUNC,0664);
	if(fd2==-1)
	{
		perror("open2");
		return -1;
	}
	int len = lseek(fd1,0,SEEK_END);
	close(fd1);
	close(fd2);
	return len;

}

int copy_file(const char *p1,const char *p2,int start,int len)
{
	int fd1,fd2;
	fd1 = open(p1,O_RDONLY);
	if(fd1==-1)
	{
		perror("open1");
		return -1;
	}
	
	fd2 = open(p2,O_WRONLY);
	if(fd2==-1)
	{
		perror("open2");
		return -1;
	}
	
	lseek(fd1,start,SEEK_SET);
	lseek(fd2,start,SEEK_SET);
	char buf[1024];
	int sum = 0;
	while(1)
	{
		int res = read(fd1,buf,sizeof(buf));
		sum+=res;//读取的总长度res大于等于文件的一半len结束
		if(sum>=len||res==0)//sum>=len 1号子进程读取长度不应该超过len,2号子进程读取到文件结尾
         {
			write(fd2,buf,res-(sum-len));
		 	break;
		 }
		write(fd2,buf,res);
	}
}
int main(int argc, const char *argv[])
{
	if(argc!=3)
	{
		printf("外部传参错误\n");
		return -1;
	}
	int len = get_len(argv[1],argv[2]);//获取源文件的长度,打开创建目标文件
	pid_t pid;
	pid = fork();
	if(pid==0)//1号子进程拷贝前一半
	{
		copy_file(argv[1],argv[2],0,len/2);	
		exit(EXIT_SUCCESS);
	}
	else if(pid>0)
	{
		pid_t pid2;
		pid2 = fork();
		if(pid2==0)//2号子进程拷贝后一半
		{
		    copy_file(argv[1],argv[2],len/2,(len-len/2));	
			exit(EXIT_SUCCESS);
		}
		else if(pid2>0)
		{
			wait(NULL);
			wait(NULL);
		}
		else
		{
			perror("fork2");
			exit(EXIT_FAILURE);
		}
	}
	else
	{
		perror("fork");
		exit(EXIT_FAILURE);

	}
	return 0;
}