C++函数与指针

最近在看C++ primer plus，感觉函数与指针这一章难点比较多，记写笔记，加强理解.

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

1. 如何声明函数指针？

和函数原型类似: 需要声明指针指向函数的返回值和参数列表

double pam(int); //参数为int 类型，返回值为double 类型的函数double (*pf);(int)  //指向参数为int类型,返回值为double 类型的指针pf = pam;   //函数名代表了函数的地址double x = pam(4); //函数名调用double x = (*pf)(4); //指针调用double x = pf(4); //C++也允许将指针名当作函数名使用

2. C++ 11 自动类型推断

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

3. 将指针名当作函数名使用

//前面函数为double *类型，cout第一部分返回double指针，第二部分返回double指针指向的值cout<<(*p1)(av,3)<<":"<<*(*p1)(av,3)<<endl;//和上面的cout一样只不过是使用函数指针名来调用函数cout<<p2(av,3)<<":"<<*p2(av,3)<<endl;

4. 函数指针数组

const double *(*pa[3]) (const double *,int) = {f1,f2,f3}; //创建函数指针数组//通过指针调用函数，得到返回的指针const double *px = pa[0](av,3); //call by pointer as if it were a function nameconst double *py = (*pa[0])(av,3); //正常调用//得到函数返回指针指向的值double x = *pa[0](av,3);double x = *(*pa[0])(av,3);

5. 指向指针数组的指针

指针数组和数组指针的区别

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

指向数组的指针

1 auto pc = &pa; //&pa是整个数组的地址, pa是数组第一个元素首地址

3 const double * (*(*pd)[3])(const double *, int ) = &pa; //和第一个等价

5 **&pa = *pa = pa[0]

代码：

//arfupt.cpp -- an array of function pointers#include<iostream>//various notations,same signaturesconst double *f1(const double ar[],int n);const double *f2(const double [],int);const double *f3(const double *,int);int main(){    using namespace std;    double av[3] = {1112.3,1542.6,2227.9};    //pointer to a function    const double *(*p1)(const double *,int) = f1;    auto p2 = f2;//C++ 11 utomatic  type deduction    //pre-C++11 can use the following code instead    //const double *(*p2)(const double *,int) = f2;    cout<<"Using pointers to functions:\n";    cout<<"Address Value\n";    cout<<(*p1)(av,3)<<":"<<*(*p1)(av,3)<<endl;    cout<<p2(av,3)<<":"<<*p2(av,3)<<endl;    //pa an array of pointers    //auto doesn't work with list initialization    const double *(*pa[3])(const double *,int) = {f1,f2,f3};    //pb a pointer to first element of pa    auto pb = pa;    // pre-C++11 can use the following code instead    // const double *(**pb)(const double *, int) = pa;    cout<<"\nUsing an array of pointers to functions:\n";    cout<<"Address Value\n";    for(int i = 0;i < 3; i++)        cout<<pa[i](av,3)<<":"<<*pa[i](av,3)<<endl;    cout<<"\nUsing a pointer to a pointer to a function:\n";    cout<<"Address Value\n";    for(int i = 0;i < 3; i++)        cout<<pb[i](av,3)<<":"<<*pb[i](av,3)<<endl;    //what about a pointer to an array of function pointers    cout<<"\nUsing pointers to an array of pointers:\n";    cout<<"Address Value\n";    //easy way to declare pc    auto pc = &pa;    // pre-C++11 can use the following code instead    // const double *(*(*pc)[3])(const double *, int) = &pa;    cout<<(*pc)[0](av,3)<<":"<<*(*pc)[0](av,3)<<endl;    //hard way to declare pd    const double *(*(*pd)[3])(const double *,int) = &pa;    //store return value in pdb    const double *pdb = (*pd)[1](av,3);    cout<<pdb<<":"<<*pdb<<endl;    //alternative notation    cout<<(*(pd)[2])(av,3)<<":"<<*(*(*pd)[2])(av,3)<<endl;}const double * f1(const double * ar, int n){return ar;}const double * f2(const double ar[], int n){return ar+1;}const double * f3(const double ar[], int n){return ar+2;}

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