Appending BSTR in a LPCSTR

Question

I have a class function which is receving a BSTR. In my class I have a member variable which is LPCSTR. Now I need to append BSTR ins LPCSTR. How I can do that. Here is my function.

void MyClass::MyFunction(BSTR text)
{
    LPCSTR name = "Name: ";
    m_classMember = name + text; // m_classMember is LPCSTR.
}

in my m_classMember I want that after this function value should be "Name: text_received_in_function". How i can do that.

Answer 1

Use the Microsoft specific _bstr_t class, which handles the ANSI/Unicode natively. Something like

#include <comutils.h>
// ...

void MyClass::MyFunction(BSTR text)
{
    _bstr_t name = "Name: " + _bstr_t(text, true);
    m_classMember = (LPCSTR)name;
}

is what you almost want. However, as pointed out by the remarks, you have to manage the lifetime of m_classMember and the concatened string. In the example above, the code is likely to crash.

If you own the MyClass object, you could simply add another member variable:

class MyClass {
private:
  _bstr_t m_concatened;
//...
};

and then use m_classMember as a pointer to the string content of m_concatened.

void MyClass::MyFunction(BSTR text)
{
    m_concatened = "Name: " + _bstr_t(text, true);
    m_classMember = (LPCSTR)m_concatened;
}

Otherwise, prior to the assignment of m_classMember, you should free it in the same way you allocated it (free, delete [], etc), and create a new char* array in which you copy the content of the concatened string. Something like

void MyClass::MyFunction(BSTR text)
{
    _bstr_t name = "Name: " + _bstr_t(text, true);

    // in case it was previously allocated with 'new'
    // should be initialized to 0 in the constructor
    delete [] m_classMember; 
    m_classMember = new char[name.length() + 1];

    strcpy_s(m_classMember, name.length(), (LPCSTR)name);
    m_classMember[name.length()] = 0;
}

should do the work.