创建子父进程，子进程将1.txt内容拷贝到2.txt中，父进程将3.txt内容拷贝到4.txt中。

#include <myhead.h>

int main(int argc, const char *argv[])
{
	pid_t ID;
	ID = fork();
	if(ID>0)//父进程
	{
		printf("父进程ID:%d\n",ID);
		int fd = open("3.txt",O_RDONLY);//只读打开
		int fd1 = open("4.txt",O_WRONLY|O_CREAT|O_TRUNC,0664);//只写打开
		if(fd == -1 && fd1 == -1)
		{
			perror("");
			return -1;
		}
		while(1)
		{
			char ch[5] = {0};
			int len = read(fd,ch,sizeof(ch));//读取字符串
			write(fd1,ch,len);//写入字符串
			if(len != sizeof(ch))
			{
				break;
			}
		}
		close(fd);
		close(fd1);
		fd1 = open("4.txt",O_RDONLY);
		char str[32] = {0};
		read(fd1,str,sizeof(str));//看写入的内容
		printf("%s",str);
		puts("**************");
	}
	//子父进程独立进行
	else if(ID == 0)//子进程
	{
		printf("子进程ID:%d\n",ID);
		int fd = open("1.txt",O_RDONLY);
		int fd1 = open("2.txt",O_WRONLY|O_CREAT|O_TRUNC,0664);
		if(fd == -1 && fd1 == -1)
		{
			perror("");
			return -1;
		}
		while(1)
		{
			char ch[5] = {0};
			int len = read(fd,ch,sizeof(ch));
			write(fd1,ch,len);
			if(len != sizeof(ch))
			{
				break;
			}
		}
		close(fd);
		close(fd1);
		fd1 = open("2.txt",O_RDONLY);
		char str[32] = {0};
		read(fd1,str,sizeof(str));
		printf("%s",str);
	}
	else
	{
		perror("fork");
		return -1;
	}
	return 0;
}

运行结果

整理整理