read/writeシステムを使用してレプリケーションファイルを呼び出す

 //NOTE: unistd.h header file should be included at first
// for other header files  would depend on it
#include 
#include 
#include 
#include 
#include 

//for files
#include 
#include 
#include 

#define  STD_FILE_INPUT		0
#define  STD_FILE_OUTPUT	1
#define  STD_FILE_ERROR		2

#define  EACH_UNIT 128

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

	const char *src_file = "./draft1.txt";
	const char *dest_file = "./draft2.txt";

	//open two files
	int fd_src = open(src_file, O_RDONLY);
	if(fd_src == -1){
		char err[128];
		sprintf(err, "open src file failed, errno = %d 
", errno);
		write(STD_FILE_OUTPUT, err, strlen(err)+1);
		return -1;
	}

	int fd_dest = open(dest_file, O_WRONLY | O_CREAT,  S_IWUSR | S_IRUSR);

	if(fd_dest == -1){

		char err[128];
		sprintf(err, "open [O_WRONLY] dest file failed, errno = %d 
", errno);
		write(STD_FILE_OUTPUT, err, strlen(err)+1);
		

		fd_dest = open(dest_file, O_CREAT, S_IWUSR | S_IRUSR);

		if(fd_dest == -1) {
			char err[128];
			sprintf(err," create [ S_IWUSR | S_IRUSR]  dest file failed, errno = %d 
", errno);
			write(STD_FILE_OUTPUT, err, strlen(err)+1);
			close(fd_src);
			return -1;
		}

	}

	int nread = 1;

	while(nread){

		
		char c ; 
		//nread = read(fd_src, &c, sizeof(c));


		char data[EACH_UNIT] = {0};
		nread = read(fd_src, &data, sizeof(data));

		if(-1 != nread){

			//fd_src+=nread;
			printf("[while] - nread :%d 
", nread );

			//        ，        
			//int nwrite = write(fd_dest, &c, nread); 
			int nwrite = write(fd_dest, &data, nread); 

			printf("[while] - nwrite :%d 
", nwrite );

			if(nwrite == -1){

				const char * err_msg_write = "write error
";
				write(STD_FILE_OUTPUT, err_msg_write, sizeof(err_msg_write)/ sizeof(err_msg_write[0]));

				close(fd_dest);
				close(fd_src);

				return -2;
			}
			
			//fd_dest+=nwrite;
			

		}else{

			const char * err_msg_read = "read error
";
			write(STD_FILE_OUTPUT, err_msg_read, sizeof(err_msg_read)/ sizeof(err_msg_read[0]));

			close(fd_dest);
			close(fd_src);

			return -3;
		}
	}//while

	//close both file handles
	close(fd_dest);
	close(fd_src);

	return 0;
}


/*
      

[queyue@localhost file-system]$ TIMEFORMAT="" time ./test-copy-system 
[while] - nread :128 
[while] - nwrite :128 
[while] - nread :14 
[while] - nwrite :14 
[while] - nread :0 
[while] - nwrite :0 
0.00user 0.00system 0:00.00elapsed ?%CPU (0avgtext+0avgdata 432maxresident)k
0inputs+0outputs (0major+141minor)pagefaults 0swaps


*/