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Comments on Is it UB to read value of heap pointer after freeing?
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Is it UB to read value of heap pointer after freeing?
I've read in a guide that "the use of indeterminate memory for anything, including apparently harmless comparison or arithmetic, can have undefined behavior if the value can be a trap representation for the type."
The included quote from C11, section 6.2.4 §2, says:
The value of a pointer becomes indeterminate when the object it points to (or just past) reaches the end of its lifetime.
The reason I'm mentioning the quote here is partially because I don't have a copy of the C standard.
Is reading the value of a pointer returned by a heap allocation function after its deallocation truly an instance of undefined behavior? (For example, debuggers may read and output the address to various I/O destinations: printer, screen, disk, network, etc.)
Consider the following program:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
void *pointer = malloc(1);
if (pointer == NULL) return 1;
free(pointer);
printf("%p\n", pointer); /* Reading the address. Undefined behavior? */
return 0;
}
Does the specification for this differ across ANSI C and other versions of ISO C?
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