[C ++] functions, pointers, and function pointers

[C ++] functions, pointers, and function pointers

Recently, I have been reading C ++ primer plus. I feel that there are many difficulties in the chapter of functions and pointers. I want to take notes and enhance my understanding.

From C ++ Primer Plus: Chapter 7 Function: C ++ Programming Modules

1. How to declare a function pointer?

Similar to the function prototype: You need to declare the pointer to the function's return value and parameter list.

Double pam (int); // The parameter is of the int type, and the return value is of the double type. The double (* pf) function; (int) // point to the int type parameter, the pointer pf = pam whose return value is double type; // The function name represents the function address double x = pam (4); // The function name calls double x = (* pf) (4); // the pointer calls double x = pf (4); // C ++ also allows the pointer name to be used as the function name

 

2. C ++ 11 automatic type inference

const double * f1(const double *, int);const double * (*p1)(const double *, int); //p1 poitns to f1auto p2 = f1; //C++11 automatic type deduction,p2 points to f1 as well

 

3. Use the pointer name as the function name

// The preceding function is of the double * type. The first part of cout returns the double pointer, and the second part returns the value cout pointed to by the double pointer <(* p1) (av, 3) <": "<* (* p1) (av, 3) <endl; // same as the preceding cout, it only uses the function pointer name to call the function cout <p2 (av, 3) <":" <* p2 (av, 3) <endl;

 

4. function pointer Array

Const double * (* pa [3]) (const double *, int) = {f1, f2, f3}; // create a function pointer array // call a function through a pointer, returns the pointer const double * px = pa [0] (av, 3 ); // call by pointer as if it were a function nameconst double * py = (* pa [0]) (av, 3 ); // normal call // obtain the value pointed to by the pointer returned by the function. double x = * pa [0] (av, 3); double x = * (* pa [0]) (av, 3 );

 

5. pointer to the pointer Array

Differences between pointer arrays and array pointers

*pd[3] //an array of 3 pointers(*pd)[3] //a pointer to an array of three elements

 

Pointer to array

1 auto pc = & pa; // & pa is the address of the entire array, and pa is the first address of the array element 2 3 const double * (* pd) [3]) (const double *, int) = & pa; // equivalent to the first 4 5 ** & pa = * pa = pa [0]

 

Code:

 1 //arfupt.cpp -- an array of function pointers 2 #include<iostream> 3 //various notations,same signatures 4 const double *f1(const double ar[],int n); 5 const double *f2(const double [],int); 6 const double *f3(const double *,int); 7  8 int main() 9 {10     using namespace std;11     double av[3] = {1112.3,1542.6,2227.9};12 13     //pointer to a function14 15     const double *(*p1)(const double *,int) = f1;16     auto p2 = f2;//C++ 11 utomatic  type deduction17     //pre-C++11 can use the following code instead18     //const double *(*p2)(const double *,int) = f2;19     cout<<"Using pointers to functions:\n";20     cout<<"Address Value\n";21     cout<<(*p1)(av,3)<<":"<<*(*p1)(av,3)<<endl;22     cout<<p2(av,3)<<":"<<*p2(av,3)<<endl;23 24     //pa an array of pointers25     //auto doesn't work with list initialization26     const double *(*pa[3])(const double *,int) = {f1,f2,f3};27     //pb a pointer to first element of pa28     auto pb = pa;29     // pre-C++11 can use the following code instead30     // const double *(**pb)(const double *, int) = pa;31     cout<<"\nUsing an array of pointers to functions:\n";32     cout<<"Address Value\n";33     for(int i = 0;i < 3; i++)34         cout<<pa[i](av,3)<<":"<<*pa[i](av,3)<<endl;35     cout<<"\nUsing a pointer to a pointer to a function:\n";36     cout<<"Address Value\n";37     for(int i = 0;i < 3; i++)38         cout<<pb[i](av,3)<<":"<<*pb[i](av,3)<<endl;39 40     //what about a pointer to an array of function pointers41     cout<<"\nUsing pointers to an array of pointers:\n";42     cout<<"Address Value\n";43     //easy way to declare pc44     auto pc = &pa;45     // pre-C++11 can use the following code instead46     // const double *(*(*pc)[3])(const double *, int) = &pa;47     cout<<(*pc)[0](av,3)<<":"<<*(*pc)[0](av,3)<<endl;48     //hard way to declare pd49     const double *(*(*pd)[3])(const double *,int) = &pa;50     //store return value in pdb51     const double *pdb = (*pd)[1](av,3);52     cout<<pdb<<":"<<*pdb<<endl;53     //alternative notation54     cout<<(*(pd)[2])(av,3)<<":"<<*(*(*pd)[2])(av,3)<<endl;55 }56 57 const double * f1(const double * ar, int n)58 {59 return ar;60 }61 const double * f2(const double ar[], int n)62 {63 return ar+1;64 }65 const double * f3(const double ar[], int n)66 {67 return ar+2;68 }