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From: vesa_karvonen (vesa_karvonen_at_[hidden])
Date: 2002-01-24 11:06:29

I just committed a fun preprocessor example into the CVS.

The DELAY() macro implemented in the example source takes exponential
time to expand into nothing. For instance, on the 800MHz PIII I use
at the office, it takes roughly 4 seconds to compile delay.cpp like
this on the MSVC++ compiler:

cl -Zs -nologo -I../../.. -DDELAY_MAX=15 delay.cpp

The maximum argument to delay is 50. This means that if I use the

cl -Zs -nologo -I../../.. -DDELAY_MAX=50 delay.cpp

It takes roughly 4000 years to complete.

As an interesting technical detail, DELAY() takes a constant amount
of memory to compile. Similar delaying tricks can be done using
template metaprogramming, but they do not work very well, because
template instantiation takes a lot of memory, so eventually the
computer runs out of memory.

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