Linux下的C语言编程——系统调用read和write函数实现文件拷贝

川长思鸟来 2022-07-15 11:18 247阅读 0赞

系统调用read和write函数实现文件拷贝

#include <stdio.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcnyl.h>
    #include <stdlib.h>
    #include <errno.h>
    
    #define SIZE 1024
    
    int main()
    {
    	int from_fd;
    	int to_fd;
    
    	int nread;
    	int nwrite;
    
    	char buff[SIZE];
    	char *ptr;
    
    	if(argc != 3)
    	{
    		fprintf(stderr,"Usage: %s fromfile tofile\n\a",argv[0]);
    		exit(-1);
    	}
    
    	if((from_fd = open(argv[1],O_RDONLY)) == -1)
    	{
    		fprintf(stderr,"open %serror: %s\n",argv[1],strerror(errno));
    		exit(-1);
    	}
    	
    	if((to_fd = open(argv[2],O_WRONLY|O_CREAT,S_IRUSR|S_IWUSR)) == -1)
    	{
    		fprintf(stderr,"open %serror: %s\n",argv[2],strerror(errno));
    		exit(-1);
    	}
    
    	while(nread = read(from_fd,buffer,SIZE))
    	{
    		if((nread == -1) && (errno != EINTR))
    		{
    			break;
    		}
    		else
    			if(nread > 0)
    			{
    				ptr = buffer;
    
    				while(nwrite = write(to_fd,ptr,nread))
    				{
    					if((nwrite == -1) && (errno != EINTR))
    					{
    						break;
    					}
    					else
    						if(nwrite == nread)
    						{
    							break;
    						}
    						else
    							if(n_write > 0)
    							{
    								ptr += nwrite;
    								nread -= nwrite;
    							}
    				}
    
    				if(nwrite == -1)
    				{
    					break;
    				}
    
    			}
    	}
    
    	close(from_fd);
    	close(to_fd);
    	exit(0);
    
        return 0;
    }