Usage of CoTaskMemAlloc?

Question

When is it appropriate to use CoTaskMemAlloc? Can someone give an example?

Answer 1

Use CoTaskMemAlloc when returning a char* from a native C++ library to .NET as a string.

C#

[DllImport("test.dll", CharSet=CharSet.Ansi)]
extern static string Foo();

C

char* Foo()
{
    std::string response("response");
    int len = response.length() + 1;
    char* buff = (char*) CoTaskMemAlloc(len);
    strcpy_s(buff, len, response.c_str());
    return buff;
}

Since .NET uses CoTaskMemFree, you have to allocate the string like this, you can't allocate it on the stack or the heap using malloc / new.