Copy file with hole

最新推荐文章于 2025-11-25 21:49:23 发布

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#file #output #buffer #input #测试

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本文介绍了一个类似于cp命令的实用程序，该程序在复制含有空洞的文件时，能够跳过空字节而不写入输出文件，有效节省存储空间。文中详细展示了实现这一功能的C语言代码示例。

Write a utility like cp(1) that copies a file containing holes, without writing the bytes of 0 to the output file.

#include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <string.h> #include <sys/stat.h> #define BSIZE 4096 #define RWRWRW (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH) int main(int argc, char * argv[]) { int srcfd; int destfd; char rdbuf[BSIZE]; char wrbuf[BSIZE]; ssize_t size; int i; int buf_offset = 0; int hole_offset = 0; if(argc != 3) { printf("Input should be like: cp src_file dest_file/n"); return; } if((srcfd = open(argv[1],O_RDONLY)) < 0) { printf("Open %s error/n",argv[1]); } if((destfd = open(argv[2],O_WRONLY|O_CREAT|O_TRUNC,RWRWRW)) < 0) { printf("Creat %s error/n",argv[2]); } while((size = read(srcfd, rdbuf, BSIZE)) > 0) { memset(wrbuf,0,BSIZE); i = 0; for(;i<size;i++) { if(rdbuf[i] == 0) { if(hole_offset == 0 && wrbuf > 0) { if(write(destfd,wrbuf,buf_offset)<buf_offset) { printf("Write error/n"); } buf_offset = 0; memset(wrbuf,0,BSIZE); } hole_offset++; } else if(hole_offset > 0) { if(lseek(destfd,hole_offset,SEEK_CUR) < 0) { printf("Lseek error/n"); } hole_offset = 0; wrbuf[buf_offset++] = rdbuf[i]; } else { wrbuf[buf_offset++] = rdbuf[i]; } } if( hole_offset > 0) { if(lseek(destfd,hole_offset,SEEK_CUR) < 0) { printf("Left lseek error/n"); } hole_offset = 0; } if( buf_offset > 0) { if(write(destfd,wrbuf,buf_offset) < buf_offset) { printf("Left write error/n"); } buf_offset = 0; } } }

在copy过程中使用了buffer，测试通过！