CODEWITHSUNDEEP
c++
goaran
goaran

Reputation: 495

c++ call of virtual base function is ignored

i have a base class 

class DLL_IMPORTEXPORT Base
{
public:
    explicit Base(Base *parentItem = NULL);
    virtual ~Base();
    virtual bool initFromXml(const pugi::xml_node &xml_node);
    //....
};

as well as a derived class

class DLL_IMPORTEXPORT Derived : public Base
{
public:
    Derived(Base *parentItem = 0);
    ~Derived();

    bool initFromXml(const pugi::xml_node &xml_node);
    //...
};

now i want to call the base class method

virtual bool initFromXml(const pugi::xml_node &xml_node);

from the derived class method

bool Derived::initFromXml(const pugi::xml_node &xml_node)
{
    bool all_ok = false;

    // .... do some specific things

    // then run the base class method
    all_ok = all_ok && Base::initFromXml(xml_node);

    return all_ok;
}

It all compiles fine, however, when i execute the code the base class methode is not executed and when i try to step into it in the debugger it does't step into it and just ignores it. I'm a bit confused. where is my brain-bug?

Upvotes: 3

Views: 81

Answers (1)

jfMR
jfMR

Reputation: 24788

The expression:

all_ok && Base::initFromXml(xml_node)

uses the logical operator && which has short-circuit evaluation, i.e.: if all_ok is false Base::initFromXml() won't called, since the result of the whole expression can be already determined: false.

If you really want to call Base::initFromXml() regardless of the value of all_ok, then you can either swap the order of the operands in the expression above, that is:

Base::initFromXml(xml_node) && all_ok

or call the function in a separate statement and save its return value:

...
bool res_init = Base::initFromXml(xml_node);
all_ok = all_ok && res_init;

As suggested in this comment, using the bitwise and-operator (&) instead of the logical and-operator (&&) would be also a solution, since it does not short-circuit:

all_ok = all_ok & Base::initFromXml(xml_node);

Upvotes: 8

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