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Comments on Behavior of Pointer Arithmetic on the Stack
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Behavior of Pointer Arithmetic on the Stack
Consider the following code:
#include <stdio.h>
int main() {
int a = 5;
int b;
++*(&b + 1);
printf("%d\n", a);
return 0;
}
The output is as expected:
6
By creating and incrementing a pointer to b, I'm able to access a, since b is below a on the stack. Is this behavior guaranteed by the C language, or is this undefined/unspecified behavior? If UB, what does the standard have to say that disallows this? For example, does C guarantee that the stack grows downwards, or that arithmetic with pointers into the stack is valid?
This is absolutely undefined behavior. The C standard doesn't say anything about stacks or how they should behave or …
2y ago
Generally speaking, pointer arithmetic is undefined behavior unless carried out on arrays. This is how the additive oper …
2y ago
I'm able to access a, since b is below a on the stack. No, it's not! You have no guarantee in what order the compi …
2y ago
Not only does the C language not guarantee it, it also will fail on actual compilers, as soon as you enable optimisation …
2y ago
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