Comment on Write a program that makes 2 + 2 = 5parentComments−wenderen12yI think the line above the printf call should be arr[2] = 3; I ran your program and I got 4. Then I changed arr[1] to arr[2] and got 5, as I expected.−Kenji12yIt's only likely, but not certain that a or b get overwritten. How your stack is laid out is entirely up to the compiler. arr[1] is already out of bounds, however, we don't know for certain what's immediately above the array.−codeflo12yWith compiler optimizations turned on, it's almost guaranteed not to happen, because a and b are very likely to be stored in CPU registers.−mgraczyk12yOr rather, a and b will be constant folded so that the printf call is optimized to "push #4; push ptrFmt; call printf"−Someone12yA truly good compiler would replace that printf by a call to putchar or pass a constant string to 'write' (gcc almost (?) does that. See http://www.ciselant.de/projects/gcc_printf/gcc_printf.html)−wyager12yThe compiler is probably aligning all stack elements to 8 bytes.
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I think the line above the printf call should be
I ran your program and I got 4. Then I changed arr[1] to arr[2] and got 5, as I expected.It's only likely, but not certain that a or b get overwritten. How your stack is laid out is entirely up to the compiler. arr[1] is already out of bounds, however, we don't know for certain what's immediately above the array.
With compiler optimizations turned on, it's almost guaranteed not to happen, because a and b are very likely to be stored in CPU registers.
Or rather, a and b will be constant folded so that the printf call is optimized to "push #4; push ptrFmt; call printf"
A truly good compiler would replace that printf by a call to putchar or pass a constant string to 'write' (gcc almost (?) does that. See http://www.ciselant.de/projects/gcc_printf/gcc_printf.html)
The compiler is probably aligning all stack elements to 8 bytes.