Besides VC6 still be the fastest Microsoft's compiler, It is not C/C++ standard compliant. Because of that, Microsoft modified their compiler several times. Since VC8, Microsoft claims that their compiler is 100% C/C++ compliant with the standards. When you are focusing softwares only for Windows, to use VC6 is not an issue. But, if you are doing something that needs to be portable on several operating systems, VC6 can lead you at wrong results. The best thing, in that case, is you to choose an slower but most standard compliant compiler: GCC. One think must be said: there is none compiler 100% standard compliant. That is the fact.

Alessandro Antonello