1，思维导图

2，用两个进程分别复制文件的上下两部分到另一个文件

#include<myhead.h>
int main(int argc, const char *argv[])
{
	int fp=open("./1.txt",O_RDONLY);
	if(fp==-1)
	{
		perror("open");
		return -1;
	}
	int count=lseek(fp,0,SEEK_END);
	close(fp);
	pid_t pid1;
	pid1=fork();
	if(pid1==0)
	{
		char str1[5];
		int fp1=open("1.txt",O_RDONLY);
		int fp2=open("2.txt",O_WRONLY|O_CREAT|O_TRUNC,0664);
		int siz_read1=0;
		int siz_read2=0;
	while(siz_read2<count/2&&((siz_read1=read(fp1,str1,sizeof(str1)))>0))
	{
		siz_read2+=siz_read1;
		write(fp2,str1,siz_read1);
	}
	close(fp1);
	close(fp2);
	exit(EXIT_SUCCESS);
	}
	else if(pid1>0)
	{
		pid_t pid2;
		pid2=fork();
		if(pid2==0)
		{
		char str1[5];
		int fp1=open("1.txt",O_RDONLY);
		int fp2=open("2.txt",O_WRONLY);
		lseek(fp1,count/2,SEEK_SET);
		lseek(fp2,count/2,SEEK_SET);
		int siz_read1=0;
	while((siz_read1=read(fp1,str1,sizeof(str1)))>0)
	{
		write(fp2,str1,siz_read1);
	}
	close(fp1);
	close(fp2);
	exit(EXIT_SUCCESS);
		}
		else if(pid2>0)
		{
			waitpid(pid1,NULL,0);
			waitpid(pid2,NULL,0);
			exit(EXIT_SUCCESS);
		}
	}
	return 0;
}