Why Does My Program Crash with a 'Pure Virtual Function Call' Error?

Unraveling the Mystery of "Pure Virtual Function Call" Crashes

In the digital realm, crashes are an unavoidable nuisance that can leave users scratching their heads. Among these baffling errors, "pure virtual function call" stands out as one particularly perplexing enigma.

This issue arises when an object creation attempt for an abstract class fails, leaving users wondering how such programs compile at all. However, the culprit lies not in the abstract nature of the class but rather in an attempt to invoke a virtual function from within a constructor or destructor.

As illustrated in the snippet of code below, such an attempt is a programming faux pas:

class Base
{
public:
    Base() { reallyDoIt(); }
    void reallyDoIt() { doIt(); } // DON'T DO THIS
    virtual void doIt() = 0;
};

class Derived : public Base
{
    void doIt() {}
};

int main(void)
{
    Derived d;  // This will cause "pure virtual function call" error
}

Here, the constructor of the Base class calls the virtual function doIt(). However, since the derived class Derived has not yet been fully constructed, the virtual function table is not yet established, resulting in a call to the base class's pure virtual function, which does not exist.

This erroneous scenario leads to the dreaded "pure virtual function call" error, crashing the program.

To avoid such mishaps, it is crucial to steer clear of making virtual function calls within constructors or destructors. By adhering to this best practice, you can ensure the stability of your code and spare yourself the headache of debugging these elusive crashes.

The above is the detailed content of Why Does My Program Crash with a 'Pure Virtual Function Call' Error?. For more information, please follow other related articles on the PHP Chinese website!