UB42⚓︎

Author: Yikai Cui.

Definition⚓︎

If the quotient a/b is not representable, the behavior of both a/b and a%b (6.5.5).

a/b 的商不能表示时，a/b 和 a%b 的行为。

Description⚓︎

If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is undefined.

如果商 a/b 可以表示，表达式 (a/b)*b + a%b 的值应该等于 a；否则，a/b 和 a%b 的行为是未定义的。

Code⚓︎

UB42.c

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

int main() {
    int a = INT_MIN;
    int b = -1;
    printf("%d\n", a);
    int c = a / b;  // Undefined behavior! (1)
    printf("%d", c);
}

Undefined behavior! The quotient a/b is actually INT_MAX + 1, which is not representable, whatever value INT_MIN is.

View source

Configurations⚓︎

MinGWMSVC

OS: Microsoft Windows 11 22H2

gcc -v : gcc version 11.2.0 (GCC), x86_64-w64-mingw32

compile and run commands: gcc UB42.c -o UB42.exe && ./UB42.exe

OS and cl.exe version: same as UB21.1.c MSVC

compile and run commands: cl.exe /FeUB21.2 UB21.2.c && ./UB21.2.exe

Behaviors⚓︎