C Program memory map [closed]

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1. stati开发者_StackOverflow社区c int i=0; where will be the variable i allocated? Is it in BSS or initialized data segment?
2. where will be variables of storage class 'extern' and 'register' are stored?

I possible please provide code Snippet to crosscheck the above

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It's impossible to say for sure without knowing the specific implementation you're dealing with. In some cases, static int i=0; will be stored in an initialized data segment because you've supplied an initializer. In other cases, the BSS will be zero-initialized anyway, so the linker will put it there anyway. If you specified a different value (e.g., static int i=12345;) then you'd have a much better assurance of its being placed in an initialized data segment.

extern doesn't really determine where the linker will place the variable. It's pretty much as above: if the linker knows (or arranges) that BSS is zero-initialized, then something that's extern with no specified initializer may be in BSS. If BSS isn't zero-initialized, it'll normally have to be in an initialized data segment instead.

register is basically equivalent to auto -- they're both allocated at run time, typically either in a register or on the stack.

As far as verifying it, that gets to be even more dependent on the individual implementation. You'd typically find out by looking at something like a linker map file; if you want to figure it out on your own, it'll very likely involve looking at either the symbol format being used, or else spelunking the internals of the executable format for your system.

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As was said before, it depends.

In my case (gcc & Linux), I decided to go and look:

int main ( int argc, char **argv )
{
    static   int   initialized_static_var = 0;
    static   int   uninit_static_var;
    register int   reg_var;
    extern   int   extern_var;

    return 0;
}

And then objdump -x on the executable file (edited for brevity):

0804a018 l     O .bss   00000004              uninit_static_var.1704
0804a01c l     O .bss   00000004              initialized_static_var.1703

Neither the register variable nor the unused extern show up in the symbol table, which makes sense if you think about it.

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Read this: Where are static variables stored (in C/C++)?

then make your own snippets.