c++ - 错误 : invalid conversion from method to void*

Question

我正在尝试将一个方法转换为空指针，以便我可以将它用作回调方法。

void* pVoidedFunc = &testmethod;

但是我得到了错误:

error: invalid conversion from int (*)() to void*

方法是:

static int testmethod()
{
   return 0;
}

如何将方法转换为 void 指针？

Answer 1

该语言不允许将指向函数的指针自动转换为空指针。

这是 C++ 标准草案 (N3337) 关于指针转换的内容(强调我的):

4.10 Pointer conversions

2 An rvalue of type “pointer to cv T,” where T is an object type, can be converted to an rvalue of type “pointer to cv void.” The result of converting a “pointer to cv T” to a “pointer to cv void” points to the start of the storage location where the object of type T resides, as if the object is a most derived object (1.8) of type T (that is, not a base class subobject).

函数不是对象。这在:

1.8 The C+ + object model

1 The constructs in a C + + program create, destroy, refer to, access, and manipulate objects. An object is a region of storage. [Note: A function is not an object, regardless of whether or not it occupies storage in the way that objects do. ]

对象类型定义为:

3.9 Types

9 An object type is a (possibly cv-qualified) type that is not a function type, not a reference type, and not a void type.