APUE学习手札 编写一个与3.12节中dup2功能相同的函数，要求不调用fcntl函数，并且要有正确的出错处理

#include "apue.h"
#define BUFFSIZE 16
int main()
{
	char buffer[BUFFSIZE];
	int fdin,fdout,n;
	fdin=my_dup(STDIN_FILENO,3);
	fdout=my_dup(STDOUT_FILENO,4);
	if(fdin==-1||fdout==-1)
	{
		err_sys("my_dup error!");
		return -1;
	}
	else
	{
		printf("STDIN fd : %d\n", fdin);
		printf("STDOUT fd : %d\n", fdout);
		while((n=read(fdin,buffer,BUFFSIZE))>0)
		{
			if(write(fdout,buffer,n)!=n)
			{
				err_sys("write error!\n");
			}
		}
		if(n < 0)printf("read error");
	}
	return 0;
}
int my_dup(int fd,int newfd)
{

	if(fd==newfd)return fd;
	if(fd<0||fd>FOPEN_MAX)
    {
        printf("fd is wrong.\n");
        return -1;
    }
    if(newfd <0||newfd>FOPEN_MAX)
    {
        printf("newfd is wrong.\n");
        return -1;
    }
	close(newfd);
	int fileindex[newfd+1];
	int index=0;
	while((fileindex[index++]=dup(fd))!=newfd)
	{
		printf("result after dup(fd):%d\n",fileindex[index-1]);
		if(fileindex[index-1]==-1)
		{
			err_sys("my_dup error!");
			return -1;
		}
	}
	int i=0;
	for(;i<index-1;i++)
	{
		close(fileindex[i]);
	}
	return fileindex[index-1];
	
}