Initializing strings as null vs empty string

There’s a function empty() ready for you in std::string:

std::string a;
if(a.empty())
{
    //do stuff. You will enter this block if the string is declared like this
}

or

std::string a;
if(!a.empty())
{
    //You will not enter this block now
}
a = "42";
if(!a.empty())
{
    //And now you will enter this block.
}