[Open Babel] Combined code slows down

[charlie z. <zh....@gm...>]

Hello,

I am trying the code of MyChem that is based on OpenBabel. There's a
substructure match function, some declarations like

  OBMol mol;
  OBConversion conv;
  OBSmartsPattern sp;
  conv.SetInFormat("SMI");

and there are 3 lines of code following divided to 2 parts by me. I
run each part 1000 times as

code part 1 consumes 10 seconds on my laptop with Windows XP
  conv.ReadString(&mol, smiles_string);

code part 2 consumes 1 second
  sp.Init(smarts_pattern);
  molecule_match = sp.Match(mol, 1);

BUT, when I put them together and run it for 1000 times, it lasts at
least 100 seconds
for (int i=0;i<1000;i++){
  conv.ReadString(&mol, smiles_string);
  sp.Init(smarts_pattern);
  molecule_match = sp.Match(mol, 1);
}

How to explain this? Thanks.

Regards,
Charlie
zh....@gm...