dup2的实现
APUE第三章的一个习题，分享一下
1 #include <stdio.h> 2 #include <string.h> 3 #include <fcntl.h> 4 #include <unistd.h> 5 #include <errno.h> 6 7 #define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) 8 9 int mydup2 (int oldfile, int newfile) { 10 int tempfile; 11 if ((tempfile = dup(oldfile)) < 0) { 12 perror("dup(oldfile)"); 13 printf("strerror:%s\n", strerror(errno)); 14 } else { 15 close(tempfile); 16 } 17 close(newfile); 18 int tempfiles[newfile]; 19 int i; 20 for(i = 0; i < newfile; ++i) { 21 if ((tempfile = dup(oldfile)) != newfile) { 22 tempfiles[i] = tempfile; 23 } else { 24 break; 25 } 26 } 27 while(i > 0) { 28 close(tempfiles[i--]); 29 } 30 return tempfile; 31 } 32 int main(int argc, char const *argv[]) 33 { 34 int fd = open("mydup2.file", O_RDWR | O_CREAT | O_TRUNC, FILE_MODE); 35 int newfd = mydup2(fd, 20); 36 printf("fd: %d\nnewfd: %d\n", fd, newfd); 37 char wstr[] = "mydup2 test file\n"; 38 pwrite(newfd, wstr, sizeof(wstr), 0); 39 char rstr[sizeof(wstr)]; 40 pread(fd, rstr, sizeof(wstr), 0); 41 printf("%s\n", rstr); 42 return 0; 43 }
