c++ - 函数指针位移

Question

我有以下代码:

void (* point)();
point=prova;
unsigned long int imm8 = point<<24;

...
void prova(){
...
}

第三行代码我有错误:

invalid operands to binary << (have 'void (*)()' and 'int')

我试图将移位运算符应用于函数指针，但出现以下错误。我该怎么办？

Answer 1

我不明白你为什么要这样做，但错误是正确的，5.8 部分的 C++ 标准草案 Shift operators 说；

The operands shall be of integral or unscoped enumeration type and integral promotions are performed.[...]

您可以使用 reinterpret_cast如果需要，将其转换为整数类型(uintptr_t)。链接引用包含以下示例:

int i = 7;

// pointer to integer and back
uintptr_t v1 = reinterpret_cast<uintptr_t>(&i); // static_cast is an error

警告

这种类型的转换只是有条件地支持，我们可以从 C++ 草案标准部分 5.2.10 Reinterpret cast 中看到这一点，其中说:

Converting a function pointer to an object pointer type or vice versa is conditionally-supported. The meaning of such a conversion is implementation-defined, except that if an implementation supports conversions in both directions, converting a prvalue of one type to the other type and back, possibly with different cv- qualification, shall yield the original pointer value.