Linux_fileio实现copy文件

参考韦东山老师教程：https://www.bilibili.com/video/BV1kk4y117Tu?p=12

1. 通过read方式copy文件

copy文件代码：

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

/*
 * ./copy 1.txt 2.txt
 * argc    = 3
 * argv[0] = "./copy"
 * argv[1] = "1.txt"
 * argv[2] = "2.txt"
 */
int main(int argc, char **argv)
{
   
   
	int fd_old, fd_new;
	char buf[1024];
	int len;
	
	/* 1. 判断参数 */
	if (argc != 3) 
	{
   
   
		printf("Usage: %s <old-file> <new-file>\n", argv[0]);
		return -1;
	}

	/* 2. 打开老文件 */
	fd_old = open(argv[1], O_RDONLY);
	if (fd_old == -1)
	{
   
   
		printf("can not open file %s\n", argv[1]);
		return -1;