[C++] Different output from same input ( without srand() )

sylvaticus · 02-09-2008, 01:44 AM

Hello.. I have a problem with a C++ application.
Using the same input, on the same machine, without recompiling, I got most of the times very slightly similar results (but not the same) and sometimes quite different ones.

I use extensively the random_shuffle() STL algorithm and rand() calls but I never initialize the seed with srand().

My application use also an external library, GLPK, to perform optimisations..

Can anyone give me hits on this strange behaviour ???

cheers,
Antonello

dmail · 02-09-2008, 08:38 AM

So you want the same results? If so seed srand with the same constant number.

sylvaticus · 02-09-2008, 12:30 PM

Quote:

Originally Posted by dmail

So you want the same results? If so seed srand with the same constant number.

Done (srand(10) just after main() ) but still slighly different results.
20% of times -> I got EXACTLY some results (I compare two scenarios with same input data)
80% of times -> I got slighly different results