C++, function pointer

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0. Function pointers are among the most powerful tools in C.  It can be used to implement function callback in C. C++ takes a slightly different route for callbacks.

1. Function pointer

// (1)define a function

bool lengthCompare(const string&, const string&){

　　return true;

}

// (2)define a function pointer and initialize it 

bool (*pf) (const string&, const string&); 

pf = lengthCompare;

// (3)call a function through a function pointer

cmpFcn pf = lengthCompare;  // initialize the pf

pf("hi","bye"); // implicitly dereferenced 

(*pf)("hi","type"); // explicitly dereferenced 

// (4)define a type named cmpFcn, this type is a pointer to function.  

typedef bool (*cmpFcn) (const string&, const string&);

typedef int func(int*, int); // func is a function type, not a pointer to a function.

// (5)function pointer as a parameter

void useBigger(const string&, const string&, bool (*)(const string&, const string&));

void useBigger(const string&, const string&, bool (const string&, const string&));

// (6)function pointer as a return type

int (*ff(int))(int*, int); // is the same as following codes

typedef int (*pf)(int&, int);

pf ff(int); // ff return a pointer to function

// (7) example

 int main(){

　　cmpFcn pf1;
　　cmpFcn pf2 = 0; 
　　cmpFcn pf3 = lengthCompare;
　　cmpFcn pf4 = &lengthCompare;

　　pf = lengthCompare;
　　cout << pf << endl;　　 // 1
　　cout << pf1 << endl;　　// 0
　　cout << pf2 << endl;　　// 0
　　cout << pf3 << endl;　　// 1
　　cout << pf4 << endl;　　// 1

　　return 0;
}

2. There is no conversation between one pointer to function type and another. 

A function pointer must point to the function whose type is exactly the same as this pointer points to.

( Most of the code are coming from C++ primer fourth edition  )

C++, function pointer

标签：imp   roman   c++ prime   for   string   implicit   mes   call   fine   

原文地址：https://www.cnblogs.com/sarah-zhang/p/12210931.html