在C和C ++中的指针到函数和指针到对象之间转换 [英] Casts between pointer-to-function and pointer-to-object in C and C++

问题描述

我错了以下？

C ++标准说，指针到函数和指针到对象（和背面）之间的转换是条件支持与实现定义的语义，而所有C标准说，这是非法的在所有情况下，是吗？

  void foo } 
 
 int main（void）
 {
 void（* fp）（）= foo; 
 void * ptr =（void *）fp; 
 return 0; 
} 
  

ISO / IEC 14882：2011 >

5.2.10 Reinterpret cast [expr.reinterpret.cast]

8转换函数指向对象指针类型或者
反面的指针是有条件支持的。这种转换的意义是
实现定义的，除了如果一个实现支持两个方向的
转换，将一个类型的prvalue转换为
另一个类型并返回，可能具有不同的cvqualification，
会产生原始的指针值。

现在我在C标准中找不到任何东西。 ..

解决方案

没错，C（99）标准没有说明从指针到函数到指针的转换对象，因此它是未定义的行为。 ^*

---

_{*但是，定义指针到函数类型之间的行为。}

Am i wrong about the following?

C++ standards says that conversion between pointer-to-function and pointer-to-object (and back) is conditionnaly-supported with implementation-defined semantics, while all C standards says that this is illegal in all cases, right?

void foo() {}

int main(void)
{
    void (*fp)() = foo;
    void* ptr = (void*)fp;
    return 0;
}

ISO/IEC 14882:2011

5.2.10 Reinterpret cast [expr.reinterpret.cast]

8 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 cvqualification, shall yield the original pointer value.

I can't find anything about it in C standard right now...

解决方案

You're right, the C(99) standard says nothing about conversion from pointer-to-function to pointer-to-object, therefore it's undefined behaviour.^*

---

_{*Note, however, that it does define behaviour between pointer-to-function types.}

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