将一个文件读到另一个文件

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

#define BUFFER_SIZE 1024

int main(int argc, char **argv)
{
    int from_fd, to_fd;
    int read_bytes, write_bytes;
    char buffer[BUFFER_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 %s Error: %s/n",argv[1],strerror(errno));
            exit(1);
        }
    
    if((to_fd = open(argv[2],O_WRONLY|O_CREAT,S_IRUSR|S_IWUSR)) == -1)  //注意权限的设置
        {
            fprintf(stderr,"Open %s Error: %s/n",argv[2],strerror(errno));
            exit(1);
        }
    
    while(read_bytes = read(from_fd,buffer,BUFFER_SIZE))
        {
            if((read_bytes == -1) && (errno != EINTR) )
                break;
            else if(read_bytes > 0)
                {                
                    ptr=buffer;
                    while(write_bytes = write(to_fd,ptr,read_bytes))
                    {
                        if((write_bytes == -1) && (errno != EINTR))
                        break;
                        else if(write_bytes == read_bytes)
                        break;
                        else if(write_bytes > 0)
                            {
                                ptr += write_bytes;
                                read_bytes -= write_bytes;
                            }
                    }
                    if(write_bytes == -1)
                        break;            
                }    
        }
    close(from_fd);
    close(to_fd);
    exit(0);
}

 

能实现将一个存在的文件中的内容读到另外一个文件当中，另外一个文件不存在时将进行创建！

心得：注意注释的那一句，将被写入的那个文件打开的时候应该设置o_WRONLY的属性，如果设置成了O_RDONLY，内容将写不进入