1> 使用多个进程实现文件拷贝

#include<myhead.h>
int main(int argc, const char *argv[])
{
	pid_t pid;
	pid=fork();
	int fdr;
	char buf;
	if((fdr=open(argv[1],O_RDONLY))==-1)
	{
		perror("open error");
		return -1;
	}
	int len=lseek(fdr,0,SEEK_END)-lseek(fdr,0,SEEK_SET);
	int num=len/2;
	if(pid>0)
	{
		int num1,fdw;
		num1=0;
		if((fdw=open(argv[2],O_WRONLY|O_CREAT|O_TRUNC,0664))==-1)
		{
			perror("open error");
			return -1;
		}
			lseek(fdr,0,SEEK_SET);
		while(num1<num)
		{
			int res=read(fdr,&buf,sizeof(buf));
			write(fdw,&buf,res);
			num1+=res;
		}
	close(fdw);
	}
	else if(pid==0)
	{
		int fdw;
		if((fdw=open(argv[2],O_WRONLY|O_CREAT|O_APPEND,0664))==-1)
		{
			perror("open error");
			return -1;
		}
		lseek(fdr,len-num-1,SEEK_SET);
		lseek(fdw,0,SEEK_END);

		int res;
		while((res=read(fdr,&buf,sizeof(buf)))>0)
		{
				write(fdw,&buf,res);
		}
	close(fdw);

	}
	close(fdr);

	return 0;
}