strcpy_s to copy a string

I've got the following code used to copy a string to a c style string which does not work:

myFunct(const string *str)
{
    int strLen = str->length() + 1;
    char *strTemp = new char[strLen];
    strcpy_s(strTemp, sizeof(strTemp), str->c_str());
    //do something with strTemp
    delete [] strTemp;
}

The second parameter to strcpy_s, sizeof(strTemp), is too small to hold the incoming str->c_str().  It's only four bytes I'm assuming because it is a pointer.

I tried changing the sizeof call to use the dereferenced pointer as folllows, but that just returns 1 byte;
strcpy_s(strTemp, sizeof(*strTemp), str->c_str());

I could just use strLen as the size of the destination buffer, but it seems that would defeat the security.

What is the correct and secure way to copy a string to a C style string?  Any comments on this method of copying?

Thanks!