第一次调用perror（）成功，第二次返回非法搜索？

Question

I'm doing a system call to change the current directory in C++ program and for some reason first call returns success on the PERROR IN THE ELSE and the second one returns Illegal seek on the PERROR IN THE ELSE(using same command and both call to the functions will direct to the else clause). Any idea why? Thanks. I appreciate you guys' help!

void changedir(cmd_t& command, int numArg)
{
  char buffer[MAXCHAR];
  if (numArg == 1){
    chdir(getenv("HOME"));
    perror("chdir");
    getcwd(buffer, MAXCHAR);
    cout << buffer << endl;

  } else {
    chdir(command.argv[1]);
    perror("chdir");
    getcwd(buffer, MAXCHAR);
    cout << buffer << endl;

  }
}

Answer 1

Don't call perror if no error has occurred. It will give you meaningless output.

In general, the value of errno is undefined after a system/library call, unless that call documents that it sets it to a specific value. This generally only happens when the call failed and the function signaled that through its return value.

In your specific case, don't call perror unless chdir returned -1 .

On Linux, chdir will raise an EFAULT error if you give it a NULL pointer, but that's not mandated in POSIX ( chdir ), so better check the result of getenv before calling chdir (same thing for your command.argv[i] if that can potentially return a null pointer).