c++ - Webkit中的deleteOwnedPtr函数看不懂

Question

在Webkit中找到这个函数

template<typename T> inline void deleteOwnedPtr(T* ptr)
{
    typedef char known[sizeof(T) ? 1 : -1];
    if(sizeof(known))
        delete ptr;
}

为什么他们不使用

if (sizeof(T))
    delete ptr;

什么意思

char known[-1];

Answer 1

在 webkit-dev 邮件列表中找到了解释。如果有人试图删除不完整的类型，它会引发编译器错误。

https://lists.webkit.org/pipermail/webkit-dev/2010-November/015051.html

If we delete a pointer and the object has incomplete type, we get undefined behavior. Instead this code causes compilation to fail if the object has incomplete type. The use of a negative number for the size of an array is a way to guarantee we get a compilation error.