Why Does `bigCat.*pcat()` Fail to Compile When Invoking a Member Function Pointer?

Unveiling the Enigmatic Member Function Pointer Invocation

In the world of object-oriented programming, member function pointers play a crucial role in manipulating class members. However, invoking a member function through a pointer can be a perplexing task. Consider the following code snippet:

class cat {
public:
   void walk() {
      printf("cat is walking \n");
   }
};

int main(){
   cat bigCat;
   void (cat::*pcat)();
   pcat = &cat::walk;
   bigCat.*pcat();
}

Attempting to compile this code results in an error. The intriguing question remains: why does the seemingly innocuous bigCat.*pcat() statement fail to compile?

Deciphering the Problem

The answer lies in the precedence of operators. In this code snippet, the () expression has higher precedence than the .* pointer-to-member binding operator. Consequently, the compiler interprets the expression as (bigCat.*)pcat(), which is not the intended behavior.

Resolving the Conundrum

To resolve this issue, we need to explicitly specify the precedence of operations. By adding parentheses around the expression bigCat.*pcat(), we ensure that the pointer-to-member binding occurs first.

(bigCat.*pcat)();

Conclusion

With the correct placement of parentheses, the code now compiles and executes without errors. This serves as a reminder that understanding operator precedence is paramount in ensuring correct interpretation of your code.

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