经典拷贝文件代码

#include<unistd.h>
#include<fcntl.h>
#include<stdio.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 from file to file\n",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);
}
//创建目标文件
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);
}
//经典拷贝文件的代码
while(bytes_read=read(from_fd,buffer,BUFFER_SIZE))
{
//一个致命的错误发生
if((bytes_read==-1)&&(errno!=EINTR))
break;
else if(bytes_read>0)
{
ptr=buffer;
while(bytes_write=write(to_fd,ptr,bytes_read))
{
//一个致命的错误发生
if((bytes_write==-1)&&(errno!=EINTR))
break;
//写完所有读的字节
else if(bytes_write==bytes_read)
break;
//只写一部分，继续写
else if(bytes_write>0)
{
ptr+=bytes_write;
bytes_read-=bytes_write;
}
}
//写的时候发生致命的错误
if(bytes_write==-1)
break;
}
}

close(from_fd);
close(to_fd);
exit(0);
}