c - Call to fdopendir() corrupts file descriptor -


i stumbled upon problem in program working on. following reproduces issue:

#include <stdlib.h> #include <stdio.h> #include <errno.h>  #include <sys/types.h> #include <dirent.h> #include <fcntl.h> #include <sys/stat.h>  int main(int argc, char *argv[]) {     int fd, ret_fd;     dir *dirp;     fd = open("./", o_rdonly);  #if 1     if ((dirp = fdopendir(fd)) == null) {         perror("dirp");         return 1;     }     closedir(dirp); #endif      ret_fd = openat(fd, "makefile", o_rdonly);     if (ret_fd == -1) {         perror("ret_fd");         return 1;     }     return 0;  }

basically, call openat(), has been preceeded fdopendir(), fails with: bad file descriptor. however, not happen if fdopendir() omitted.

i know fdopendir() makes internal use of file descriptor, shouldn't revert changes after calling closedir()?

what can prevent openat() failing in case?

the posix description of fdopendir() says:

upon calling closedir() file descriptor shall closed.

so descriptor closed time call openat().

and a typical linux man page fdopendir():

after successful call fdopendir(), fd used internally implementation, , should not otherwise used application.


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