Question

I’m a little confused about C strings and wide C strings. For the sake of this question, assume that I using Microsoft Visual Studio 2010 Professional. Please let me know if any of my information is incorrect.

I have a struct with a const wchar_t* member which is used to store a name.

struct A
{
    const wchar_t* name;
};

When I assign object ‘a’ a name as so:

int main()
{
    A a;

    const wchar_t* w_name = L"Tom";
    a.name = w_name;

    return 0;
}

That is just copying the memory address that w_name points to into a.name. Now w_name and a.name are both wide character pointers which point to the same address in memory.

If I am correct, then I am wondering what to do about a situation like this. I am reading in a C string from an XML attribute using tinyxml2.

tinyxml2::XMLElement* pElement;
// ...
const char* name = pElement->Attribute("name");

After I have my C string, I am converting it to a wide character string as follows:

size_t newsize = strlen(name) + 1;
wchar_t * wcName = new wchar_t[newsize];
size_t convertedChars = 0;
mbstowcs_s(&convertedChars, wcName, newsize, name, _TRUNCATE);

a.name = wcName;

delete[] wcName;

If I am correct so far, then the line:

 a.name = wcName;

is just copying the memory address of the first character of array wcName into a.name. However, I am deleting wcName directly after assigning this pointer which would make it point to garbage.

How can I convert my C string into a wide character C string and then assign it to a.name?

Answer 1

The easiest approach is probably to task you name variable with the management of the memory. This, in turn, is easily done by declaring it as

std::wstring name;

These guys don’t have a concept of independent content and object mutation, i.e., you can’t really make the individual characters const and making the entire object const would prevent it from being assigned to.