c++ - 我实际上是在调用ctor并在指向对象的指针上初始化vtable吗？ C++

问这个问题我有点傻，但是我无法使用new关键字。我需要确保正在为变量Utf8Buffer所指向的对象调用构造函数，下面是一个示例。

Utf8String * pUtf8Buffer;
    void Initialize(void * stringbuffer, size_t bufferlen)
    {
        pUtf8Buffer = (Utf8String*)this->pMemMan->AllocMem(sizeof(Utf8String));
        //In the line below am I calling ctor of the object pointed to by the Utf8Buffer
        //I specifically need ctor to be called on this object to initialize the vtable
        (*pUtf8Buffer) = Utf8String(stringbuffer, bufferlen);
    }

最佳答案

相反，您需要placement new：

pUtf8Buffer = (Utf8String*)this->pMemMan->AllocMem(sizeof(Utf8String));

new (pUtf8Buffer) Utf8String(stringbuffer, bufferlen);

当然，如果构造函数抛出异常，则需要释放内存。因此，添加一个try / catch块，它具有更多类型安全性，如下所示：

void* pRawBuffer = this->pMemMan->AllocMem(sizeof(Utf8String));

try {
    pUtf8Buffer = new (pRawBuffer) Utf8String(stringbuffer, bufferlen);
} catch (...) {
    pUtf8Buffer = nullptr;
    this->pMemMan->ReleaseMem(pRawBuffer);
    throw;
}