ckd_add

#define ckd_add( result, a, b ) /* implementation-defined */
// exposed interface:
bool ckd_add( type1* result, type2 a, type3 b );

Computes the addition x + y and stores the result into *result. The addition is performed as if both operands were represented in a signed integer type with infinite range, and the result was then converted from this integer type to type1. If the value assigned to *result correctly represents the mathematical result of the operation, it returns false. Otherwise, it returns true. In this case, the value assigned to *result is the mathematical result of the operation wrapped around to the width of *result.

Parameters

Return value

false if the value assigned to *result correctly represents the mathematical result of the addition, true otherwise.

Note

Both type2 and type3 shall be any integer type other than “plain” char, bool, a bit-precise integer type, or an enumerated type, and they can be the same. *result shall be a modifiable lvalue of any integer type other than “plain” char, bool, a bit-precise integer type, or an enumerated type.

It is recommended to produce a diagnostic message if type2 or type3 are not suitable integer types, or if *result is not a modifiable lvalue of a suitable integer type.

Example

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

const char* text(bool overflow) { return overflow ? "Overflow" : "OK"; }

int main()
{
    uint8_t x;
    uint16_t y;
    uint16_t result_uint16;
    uint32_t result_uint32;
    bool overflow;

    x = 14;
    y = 28;
    overflow = ckd_add(&result_uint16, x, y);
    printf("%u + %u => %u (%s)\n", x, y, result_uint16, text(overflow));

    x = 14;
    y = UINT16_MAX;
    overflow = ckd_add(&result_uint16, x, y);
    printf("%u + %u => %u (%s)\n", x, y, result_uint16, text(overflow));

    x = 14;
    y = UINT16_MAX;
    overflow = ckd_add(&result_uint32, x, y);
    printf("%u + %u => %u (%s)\n", x, y, result_uint32, text(overflow));
}

14 + 28 => 42 (OK)
14 + 65535 => 13 (Overflow)
14 + 65535 => 65549 (OK)

References

• C23 standard (ISO/IEC 9899:2024):
• 7.20.1 The ckd_ checked integer operation macros (p: 311)

See also