Why does malloc initialize the values to 0 in gcc?

Question

Maybe it is different from platform to platform, but

when I compile using gcc and run the code below, I get 0 every time in my ubuntu 11.10.

#include         


        

Answer 1

The OS will usually clear fresh memory pages it sends to your process so it can't look at an older process' data. This means that the first time you initialize a variable (or malloc something) it will often be zero but if you ever reuse that memory (by freeing it and malloc-ing again, for instance) then all bets are off.

This inconsistence is precisely why uninitialized variables are such a hard to find bug.

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As for the unwanted performance overheads, avoiding unspecified behaviour is probably more important. Whatever small performance boost you could gain in this case won't compensate the hard to find bugs you will have to deal with if someone slightly modifies the codes (breaking previous assumptions) or ports it to another system (where the assumptions might have been invalid in the first place).