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cpointersintegerembedded

How to Cast Integer Value to Pointer Address Without Triggering Warnings

I have the following variable

uint32_t Value = 0x80

0x80 represents an address in the memory e.g.

// Write 2 at address 0x80
*(uint32_t*)((uint32_t)0x80) = 2;

How can i cast Value to a Pointer, so it points to 0x80?

uint32_t *Pointer = ?? Value;

This:

(uint32_t*)(uint32_t)Value;

returns:

warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
Solution

  • To handle integer to object pointer conversion, use the optional integer uintptr_t or intptr_t types. Function pointers are a separate matter.

    The following type designates an unsigned integer type with the property that any valid pointer to void can be converted to this type, then converted back to pointer to void, and the result will compare equal to the original pointer C11dr 7.20.1.4 1

    uintptr_t

    Then convert the void * to the desired type.

    #include <stdint.h>
uintptr_t Value = 0x80;
uint32_t *Pointer = (void *) Value;

    If 0x80 was not derived from a valid uint32_t *, the result in undefined behavior (UB). Yet it sounds like OP is on a platform with memory mapped data locations.