mmap实现大文件复制

#include <sys/mman.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdlib.h>#include <assert.h>#include <string.h>#include <stdio.h>#define BUF_SIZE 4096 int main(int argc,char *argv[]){int fd_r,fd_w;char * p_w,*p_r ;char buf[BUF_SIZE];int length_r,length_w,len = 0;int off= 0;assert(argc == 3);fd_r = open(argv[1],O_RDWR);assert(fd_r);fd_w = open(argv[2],O_RDWR|O_CREAT|O_TRUNC,0644);assert(fd_w);length_r = lseek(fd_r,0,SEEK_END);length_w = lseek(fd_w,length_r - 1,SEEK_CUR);write(fd_w,"0",1);lseek(fd_w,0,SEEK_SET);lseek(fd_r,0,SEEK_SET);//assert(p_w);while(1){p_r = mmap(NULL,BUF_SIZE,PROT_READ|PROT_WRITE,MAP_SHARED,fd_r,off);p_w = mmap(NULL,BUF_SIZE,PROT_WRITE,MAP_SHARED,fd_w,off);memcpy(p_w,p_r,BUF_SIZE);off += BUF_SIZE;if((off+BUF_SIZE) >= length_r){p_r = mmap(NULL,length_r - off ,PROT_READ|PROT_WRITE,MAP_SHARED,fd_r,off);p_w = mmap(NULL,length_r - off,PROT_WRITE,MAP_SHARED,fd_w,off);memcpy(p_w,p_r,length_r -off );munmap(p_r,length_r - off);munmap(p_w,length_r - off);break;}}close(fd_r);close(fd_w);return 0;}