Thread: declaring variables inside loops

Originally Posted by maverix

how about declaring it

Code:

static int number = 0;

I guess (not sure) it would not initialize it each time it enters the loop. Somebody please confirm :-)

maverix

Correct, it will not initialize static variables for each loop iteration (or for every call to a function for example). The compiler MAY, however, generate less good code with static variables, since there is (theoretically) a possibility that they are modified outside of the function without the compiler knowing about it. I haven't studied that much - but essentially, a static variable is a global. However, since it's limited scope, I suppose the compiler could know if the address of the static is ever exported out of the function, and thus whether it is susceptible to modification outside of the function or not.

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Mats

gcc (which is the actual compiler part of MingW) needs the switch -O to optimize, and -O2, -O3 and -O4 will make the optimization increasingly more "aggressive" (and sometimes means that code either won't work, or actually run slower). Debug mode (-g in gcc) is actually not really affecting anything other than generation of information that the debugger (gdb) can use to figure out where in the code you are executing and where to find the variables and such.

Static variables are initialized (to zero if nothing else is given as initialization) when the executable file is loaded, that's it - never ever again.

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Mats

Originally Posted by cpjust

gcc Optimization Options
-O3 is the highest one I see.

Yes, I think -O4 is actually equal to -O3 on older compilers - but gcc has moved on from 3.2.3 you know. The latest version is 4.4 or so (sorry, too lazy to look up the current latest version).

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Mats