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;
}