copyfile.c

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

#define BUFFER_SIZE 1024

int main(int argc,char **argv) {
	int from_fd,to_fd;
	int bytes_read,bytes_write;
	char buffer[BUFFER_SIZE];
	char *ptr;

	if(argc != 3) {
		fprintf(stderr,"Usage:%s fromfile tofile\n\a",argv[0]);
		exit(1);
	}

	//打开源文件
	if((from_fd = open(argv[1],O_RDONLY)) == -1) {
		fprintf(stderr,"Open %s Error:%s\n",argv[1],strerror(errno));
		exit(-1);
	}

	//创建目的文件
	if((to_fd = open(argv[2],O_WRONLY | O_CREAT,S_IRUSR | S_IWUSR)) == -1) {
		fprintf(stderr,"Open %s Error:%s\n",argv[2],strerror(errno));
		exit(1);
	}

	//经典拷贝文件代码
	while(bytes_read = read(from_fd,buffer,BUFFER_SIZE)) {
		//一个致命错误发生了
		if((bytes_read == -1) && (errno != EINTR)) 
			break;
		else if(bytes_read > 0) {
			ptr = buffer;
			while(bytes_write = write(to_fd,ptr,bytes_read)) {
				//一个致命错误发生了
				if((bytes_write == -1) && (errno != EINTR))
					break;
				//写完了所有读的字节
				else if(bytes_write == bytes_read)
					break;
				//只写了一部分,继续写
				else if(bytes_write > 0) {
					ptr += bytes_write;
					bytes_read -= bytes_write;
				}
			}

			//写得时候发生致命错误
			if(bytes_write == -1)
				break;
		}
	}
	return 0;
}