C ++：[VS2010]：警告C4396：'stdext :: hash_value'：当朋友声明时不能使用内联说明符

Question

I am converting my VS2005 C++ code to VS2010 code. Unfortunately in VS2010 it is giving compiler warning whereas in VS2005 it compiled smoothly. (FYI: I have set the warning to be treated as errors).

Pls have a look at the code snippet:

The error is at the line where the friend declaration is there.

class __declspec(dllexport) MyKey
{
    friend size_t stdext::hash_value<MyKey>(const MyKey& key);  // compiler warning at this line (pls see below for the actual compiler warning)

    ubit32  m_uKey1;

};
template<> inline size_t stdext::hash_value<MyKey>(const MyKey& key)
{
    return key.m_uKey1;
}

Here is the compiler warning as shown below:

warning C4396: 'stdext::hash_value' : the inline specifier cannot be used when a friend declaration refers to a specialization of a function template

Please help to resolve this error for me. Thanks.

Answer 1

I got the fix by adding the following two forward declaration statements before the class declaration for MyKey.

class MyKey;

template<> size_t stdext::hash_value<MyKey>(const MyKey& key);

Now the error/warning is gone. Am I doing it correctly ?

Answer 2

Since your friend declaration doesn't have the inline specifier, this is obviously a bug in MSVC compiler. You can suppress the warning with a compiler option or a pragma:

#pragma warning(disable: 4396)