Objects, Bytes, and Representation

Every object is bytes

In C, an object is a region of memory that holds a value of some type. The C standard does not say int means "a 32-bit two's complement number" — it says int has an object representation made of sizeof(int) bytes, each byte at least 8 bits (CHAR_BIT).

Three distinct notions, three different questions:

| Notion | Question | Portable answer? | | --- | --- | --- | | Type | What values can this hold? | Yes — from the standard | | Object representation | Which bytes exist? | sizeof only | | Value representation | Which bits encode the value? | No — implementation-defined |

C23 finally mandates two's complement for signed integers, but width is still implementation-defined: sizeof(int) can be 2, 4, or 8 on real platforms.

Probing your platform honestly

#include <stdio.h>
#include <limits.h>

int main(void) {
    printf("CHAR_BIT = %d\n", CHAR_BIT);
    printf("sizeof(int) = %zu\n", sizeof(int));
    printf("INT_MIN = %d\n", INT_MIN);
    return 0;
}

This program is fully portable — it prints your platform's truth rather than assuming one.

Representation is not value

For unsigned char (and all unsigned types) every bit pattern is a valid value. For signed integers C23 guarantees two's complement, but still allows padding bits in the representation — bits that exist in the object but participate in no value. memcpy-ing an object and inspecting its bytes is always valid; reading an int's representation as an int through a reinterpreted pointer is not (that journey starts in the UB module).