Just to add a little info:
GCC 4 optimizes MUCH better, than any 3.x version. I have written an image processing plugin for avisynth some time ago, and compiled with gcc 4 with -march=pentium3 -O3, it as about 2 times faster, than compiled with the EXACT same flags with gcc 3.4.5
I have also read about this, that gcc 4 uses much more modern and robust optimization techniques, and my results only confirm this.
Another thing:
Why is it needed to install gcc 4 to C:\MinGW? I tried in other directory, where I prefer, but there it cannot find it's own includes and libs. How come? Is C:\MinGW hard coded into g++.exe? (I hope not)
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Greets,
B.