catopen() does not set errno when it fails in some cases

Question

catopen is failing to open same cat file in different servers, with same setup.

When errno is 0 it means no error from my understanding.

Please tell me if anyone has seen like this before. If any one knows the reason why it is happening it will be very helpful for me

Sample code i wrote

int main()
{

   nl_catd cat;

   string fileName;

   cout<<"Enter the cat file name: ";

   cin>>fileName;

   cat = catopen(fileName.c_str(), 0);

   if (cat == (nl_catd)-1)

   {

      cerr << "Unable to open catalogue: " << fileName <<" ....and the Error number: "<<errno<<"\n";

      exit(1);

   }

   printf("File opened...\n");

   catclose( cat );

   exit(0);

}

Output for above code

For successful case:

./a.out

Enter the cat file name: LinkMonitor.epod.cat

File opened...

For faliure case:

./a.out

Enter the cat file name: ehap_ac_in.epod.cat

Unable to open catalogue: ehap_ac_in.epod.cat0

---

Here 0 is the error code.

Answer 1

You cleared errno when you wrote the string "Unable to open catalogue: " to cerr.

You have to save the value of errno straight away.

cat = catopen(fileName.c_str(), 0); 

if (cat == (nl_catd)-1) 

{ 
   int errno_catopen = errno;
   cerr << "Unable to open catalogue: " << fileName <<" ....and the Error number: "<<errno_catopen <<"\n";
   exit(errno_catopen);
}