QTS #07 - Improved attempt

#include <Windows.h>
#include <vector>

#include <iostream> //std::cout, std::endl

/////////////////////////////////////////////////////////////////

/*
/   The class is templates, put both declaration and definition in headers
/   (either both in the same file or #include the template header after the declaration)
/
/   !There might be errors, haven't slept the night :/
/
/   *required includes:
/       - vector
/       - windows.h

*/

// ------------- Declaration -------------

template <typename _TValueType = TCHAR> //Default it with TCHAR
class C_Strings
{
public:
    using value_type = std::remove_reference <
        std::remove_const<_TValueType>::type > ::type;
    using result_type = value_type;

private:

    std::vector<result_type*> m_Queue;

    result_type *AddToQueue(value_type *pValue);
    result_type *GetLastItem();

public:

    C_Strings() = default;
    ~C_Strings() {
        this->ClearQueue();
    }

    //Returns the number of elements it deleted
    size_t ClearQueue();

    //Formats a new string
    result_type *Format(value_type *fmt, ...);

    //Formats and appends to an existing string (allocates a new object, doesn't free the old one)
    result_type *FormatAppend(value_type *destination, value_type *fmt, ...);
};

// ------------- Definition -------------

template <typename _TValueType>
auto C_Strings<_TValueType>::AddToQueue(value_type *pValue) -> result_type * {
    this->m_Queue.push_back(pValue);
    return pValue;
}

template <typename _TValueType>
auto C_Strings<_TValueType>::GetLastItem() -> result_type * {
    return this->m_Queue.back();
}

template <typename _TValueType>
size_t C_Strings<_TValueType>::ClearQueue() {
    size_t counter = 0;
    for(result_type *p : m_Queue) {
        free(p);
        counter++;
    }
    return counter;
}

template <typename _TValueType>
auto C_Strings<_TValueType>::Format(value_type *fmt, ...) -> result_type * {
    va_list va;
    va_start(va, fmt);

    size_t requiredBufferSize = static_cast<size_t>(vsnprintf(nullptr, 0, fmt, va)) + 1;

    if(requiredBufferSize) {
        vsnprintf(this->AddToQueue(static_cast<value_type*>(memset(new value_type[requiredBufferSize], 0, requiredBufferSize))),
                  requiredBufferSize, fmt, va);
        return this->GetLastItem();
    }

    return nullptr;
}

template <typename _TValueType>
auto C_Strings<_TValueType>::FormatAppend(value_type *destination, value_type *fmt, ...) -> result_type * {
    va_list va;
    va_start(va, fmt);

    size_t existingBufferSize = strlen(destination);
    size_t requiredBufferSize = static_cast<size_t>(vsnprintf(nullptr, 0, fmt, va)) + 1;

    if(requiredBufferSize) {
        this->AddToQueue(static_cast<value_type*>(memset(new value_type[existingBufferSize + requiredBufferSize], 0, existingBufferSize + requiredBufferSize)));
        value_type *pBuffer = this->GetLastItem();
        value_type *pFmtBuffer = pBuffer + existingBufferSize;

        strncpy(pBuffer, destination, existingBufferSize);
        vsnprintf(pFmtBuffer, requiredBufferSize, fmt, va);

        return pBuffer;
    }

    return nullptr;
}

///////////////////////////////////////////////////////

//! Simple tests.
int main() {

    C_Strings <> x;

    std::cout << x.Format("Fmt: %s %d", "test", 1337) << std::endl;
    std::cout << x.FormatAppend("Append ", "Fmt: %s %d", "test", 1337) << std::endl;

    system("PAUSE");

}