UB23

author: Xiangzhi Liu.

Definition

Conversion of a pointer to an integer type produces a value outside the range that can be represented (6.3.2.3).

Description

将指针类型强制转换为整数类型时，如果该整数类型的值范围不足以容纳指针的值，那么行为是未定义的。

Code

UB23.c

#include <stdio.h>
int main() {
    int a;
    int* p = &a;
    unsigned char b = (unsigned char)p;  // UB. sizeof(unsigned char) == 1 and for most platform sizeof(int*) > 1
    printf("0x%X, 0x%X\n",(uintptr_t)p,b);
    return 0;
}

Configurations

Configuration 1.Configuration 2.

gcc version 4.9.2

Target: x86_64-w64-mingw32

MSVC _MSC_VER = 1928

Target: x86_64

Behaviors

Configuration 1.Configuration 2.

通过编译并产生警报 “cast from pointer to integer of different size [-Wpointer-to-int-cast]” 输出：0x62FE10, 0x10

通过编译无警报 输出：0xAFF7E0, 0xE0

Advice

如果需要将指针强转为整数，应使用 intptr_t 或 uintptr_t 类型的对象存放指针的值。