cpp(第七章)

1.c++提供了3种表示c—风格字符串方法：字符数组，字符串常量，字符串指针。其中字符数组并不一定是字符串，以空值字符''来结束的字符数组时字符串。

2.函数参数为数组时，虽然减少了时间和内存的使用，但是却使原始数据破坏风险增大，而这时候我们在函数参数数组上加上限定符const，使函数不能修改数组内容。

3.函数指针，函数名即为地址，可以定义一个参数为函数指针来传递函数地址，从而可以在函数中使用另一个函数。

4.

#include <iostream>
#include <cstdio>

const double *f1(const double ar[],int);
const double *f2(const double[],int);
const double *f3(const double * ,int);
typedef const double *(*p_fun)(const double*,int );
int main()
{
    using std::cout;
    using std::endl;
    using std::cin;
    double av[3]= {1112.3,1542.6,2227.9};
//    const double *(*pa[3])(const double *,int)= {f1,f2,f3};
//    auto pb= pa;
//    printf("%p
",f1(av,3));
//    printf("%p
",pa[0]);
//    printf("%p
",*pb[0]);
    //printf("%p
",*pa[2]);
    //cout<<long(f1)<<endl;
//    const double *(*p1)(const double*,int )= f1;
    p_fun p1= f1;
    auto p2= f2;
    cout<<"using pointers to functions:
";
    cout<<"address value
";
    cout<<(*p1)(av,3)<<" : "<<*(*p1)(av,3)<<endl;
    cout<<p2(av,3)<<" : "<<*p2(av,3)<<endl;
    const double *(*pa[3])(const double *,int)= {f1,f2,f3};
    auto pb= pa;
    cout<<"
using an array f pointer to a pointers to functions:
";
    cout<<" Address value
";
    for (int i= 0; i< 3; i++)
        cout<<pa[i](av,3)<<" : "<<*pa[i](av,3)<<endl;
    cout<<"
using a pointer to a pointer to a function:
";
    cout<<" address value
";
    for (int i= 0; i< 3; i++)
    {
        cout<<(*pb[i])(av,3)<<" : "<<*(*pb[i])(av,3)<<endl;
    }
    cout<<"
using pointers to an array of function pointers:
";
    cout<<"Address value
";
    auto pc= &pa;
    cout<<(*pc)[2](av,3)<<" : "<<*(*pc)[0](av,3)<<endl;
    const double *(*(*pd)[3])(const double *,int)= &pa;
    const double *pdb= (*pd)[1](av,3);
    cout<<pdb<<" : "<<*pdb<<endl;
    cout<<(*(*pd)[2])(av,3)<<" : "<<*(*(*pd))(av,3)<<endl;
    return 0;
}
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;
}