ckd_sub
| Defined in header <stdckdint.h>
|
||
#define ckd_sub( result, a, b ) /* implementation-defined */
// exposed interface:
bool ckd_sub( type1* result, type2 a, type3 b );
|
(since C23) | |
Computes the subtraction x - y and stores the result into *result. The subtraction 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
| a, b | - | integer values |
| result | - | address of where result should be stored |
Return value
false if the value assigned to *result correctly represents the mathematical result of the subtraction, 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>
int main()
{
int16_t result1;
constexpr int8_t x1 = -2;
constexpr int16_t y1 = 1;
const bool underflow1 = ckd_sub(&result1, x1, y1);
printf("%i - %i == %i (%s)\n", x1, y1, result1, underflow1 ? "Underflow" : "OK");
int16_t result2;
constexpr int8_t x2 = -2;
constexpr int16_t y2 = INT16_MAX;
const bool underflow2 = ckd_sub(&result2, x2, y2);
printf("%i - %i == %i (%s)\n", x2, y2, result2, underflow2 ? "Underflow" : "OK");
int32_t result3;
constexpr int8_t x3 = -2;
constexpr int16_t y3 = INT16_MAX;
const bool underflow3 = ckd_sub(&result3, x3, y3);
printf("%i - %i == %i (%s)\n", x3, y3, result3, underflow3 ? "Underflow" : "OK");
}
Output:
-2 - 1 == -3 (OK)
-2 - 32767 == 32767 (Underflow)
-2 - 32767 == -32769 (OK)
References
- C23 standard (ISO/IEC 9899:2024):
- 7.20.1 The ckd_ checked integer operation macros (p: 311)
See also
(C23) |
checked addition operation on two integers (type-generic function macro) |
(C23) |
checked multiplication operation on two integers (type-generic function macro) |
C++ documentation for ckd_sub
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