Pointer to a larger number int

Question

I have a pointer. On a 32-bit system, this is 32 bits. On a 64-bit system, this is 64 bits.

I have a long integer field used as an identifier, and sometimes I want to use a pointer value here. (I never go back to a pointer - as soon as I pass it to an integer field, I only ever compare it for equality).

For both 32-bit and 64-bit systems, this is safe. (In larger switch systems, not so). It's true?

And then is there a way to make GCC not give the following warning only when building on platforms where it is safe (that is, at the moment, all target platforms)?

error: casting to a pointer from an integer of different sizes [-Werror = int-to-pointer-cast]

Answer 1

In accordance with the standard, there is no guarantee that the pointer matches an integer type. In practice, otherwise, on most personal computers there are several memory models . You can see that pointers and integer types do not always have the same size (even on "regular" computers).

You are better off using the optional intptr_t and uintptr_t types starting with C99.

C11 (n1570), § 7.20.1.4

The following type denotes an integer type that is familiar with the property that any valid pointer to void can be converted to this type and then converted back to a pointer to void , and the result will be compared with the original pointer: intptr_t .

The following type denotes an unsigned integer type with the property that any valid pointer to void can be converted to this type and then converted back to a pointer to void , and the result is comparable to the original pointer: uintptr_t .

Here is a small example:

 #include <stdio.h> #include <stdint.h> int n = 42; int *p = &n; intptr_t i = (intptr_t)(void *)p; int *q = (void *)i; printf("%d\n", *q); 

Answer 2

If you want the integer type to be large enough to hold the pointer, consider intptr_t (signed) or uintptr_t . The standard ensures that these data types are large enough to hold the pointer. Nothing else can be accepted, especially not that long int is long enough.