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



int main(int argc, char * * argv){

	printf("输入了参数个数：%d \n",argc);
	if (argc !=3 )
	{
		printf("参数不对,useage %s file newfile \n",argv[0]);
		return -1;
	}
	//打开源文件
	int oldfile = open(argv[1],O_RDONLY);
	if (oldfile == -1)
	{
		printf("文件%s不存在！\n",argv[1]);
	}
	/* 3. 创建新文件 */
	int fd_new = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
	if (fd_new == -1)
	{
		printf("can not creat file %s \n", argv[2]);
		return -1;
	}
	char buf[1024];
	int len = 0;
	//获取输入流
	while ((len = read(oldfile,buf,1024)) > 0 )
	{
		if (write(fd_new, buf, len) != len)
		{
			printf("can not write %s\n", argv[2]);
			return -1;
		}
	}
	
	/* 5. 关闭文件 */
	close(oldfile);
	close(fd_new);
	printf("复制文件成功！\n");
	return 1;
}

主要函数：open、read、write

在linux使用： man 2 open...查看调用函数api

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/mman.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;
	struct stat stat;
	char *buf;
	
	/* 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;
	}

	/* 3. 确定老文件的大小 */
	if (fstat(fd_old, &stat) == -1)
	{
		printf("can not get stat of file %s\n", argv[1]);
		return -1;
	}

	/* 4. 映射老文件 */
	buf = mmap(NULL, stat.st_size, PROT_READ, MAP_SHARED, fd_old, 0);
	if (buf == MAP_FAILED)
	{
		printf("can not mmap file %s\n", argv[1]);
		return -1;
	}

	/* 5. 创建新文件 */
	fd_new = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
	if (fd_new == -1)
	{
		printf("can not creat file %s\n", argv[2]);
		return -1;
	}

	/* 6. 写新文件 */
	if (write(fd_new, buf, stat.st_size) != stat.st_size)
	{
		printf("can not write %s\n", argv[2]);
		return -1;
	}

	/* 5. 关闭文件 */
	close(fd_old);
	close(fd_new);
	
	return 0;
}

linux调用内核的原理图