Cocos2d-x on the strange problem of conversion between std::string and const char*

First, a string type data
    Ccuserdefault::shareduserdefault ()->setstringforkey ("Jason", "Hello") is stored;
    Ccuserdefault::shareduserdefault ()->flush ();
    
    Then get
    the string const char* FileName = Ccuserdefault::shareduserdefault ()->getstringforkey ("Jason") by the following way. C_STR () ;
    The print statement is normal and the output is Hello
    cclog ("filename:%s", fileName);
    But the following statement appears on the device on the error, or nothing, or the string is incomplete, or display Helvetica
    cclabelttf* label = cclabelttf::create (FileName, "Helvetica", );
    Label->setposition (CCP ());
    AddChild (label);

Then to solve the above problem, we change the way 
    cclabelttf* label = Cclabelttf::create (Ccuserdefault::shareduserdefault () Getstringforkey ("Jason"). C_str (), "Helvetica", "(");
    Label->setposition (CCP ());
    AddChild (label); The result is Hello, normal

Let's put it another way 
    std::string fileName = Ccuserdefault::shareduserdefault ()->getstringforkey ("Jason");
    cclabelttf* label = Cclabelttf::create (Filename.c_str (), "Helvetica", +);
    Label->setposition (CCP (240, 160)); The results are also Hello, normal

Another way to do it 
    std::string fileName = Ccuserdefault::shareduserdefault ()->getstringforkey ("Jason");
    Const char* file = Filename.c_str ();
    cclabelttf* label = cclabelttf::create (file, "Helvetica",);
    Label->setposition (CCP ());
    AddChild (label);
    As a result, the writing is also normal, then why the most up-to-do not get the correct results?

Summary: Although the underlying reasons do not know, but you can first remember: return std::string type is used std::string type to connect

My cocpos2d-x version cocos2d-2.1rc0-x-2.1.2, there are children's shoes to know why please enlighten.