通用算法之可调整的函数对象

1,实例代码:

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
using namespace std;

//自定义可以调整的函数对象
class MyAdd : public binary_function<int,int,int>
{
public:
    MyAdd(){}
    //注意const
    int operator()(int m,int n) const
    {
        return m+n;
    }
};

bool isOdd(int d){ return d&0x01; }
int myAdd(int m,int n ){ return m+n; }

int main()
{
  ostream_iterator<int> out(cout, " ") ;
  int a[]={1,3,4,5,8,9};
  int size=sizeof(a)/sizeof(a[0]);
  transform(a,a+size,a,bind2nd(MyAdd(),100));
  copy(a,a+size,out);
  cout<<endl;
  /*
  ptr_fun的使用:将函数转化为函数对象,函数必须是一元或二元函数
  */
  //判断是否为偶数
  vector<bool> vb;
  transform(a,a+size,back_inserter(vb),not1(ptr_fun(isOdd)));
  copy(vb.begin(),vb.end(),out);
  cout<<endl;
  //实现了相同的功能,加一个数
  vector<int> vecint;
  transform(a,a+size,back_inserter(vecint),bind1st(ptr_fun(myAdd),1000));
  copy(vecint.begin(),vecint.end(),out);
  cout<<endl;
}

2,mem_fun:序列元素为对象的指针,将成员函数转化为函数对象.
mem_fun_ref:序列元素为对象,将成员函数转化为函数对象.
实例代码1:

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
using namespace std;

class Shape
{
public:
    virtual void draw() = 0;
    virtual ~Shape() {}
};

class Circle : public Shape
{
public:
    virtual void draw() { cout << "Circle::Draw()" << endl; }
    ~Circle() { cout << "Circle::~Circle()" << endl; }
};

class Square : public Shape
{
public:
    virtual void draw() { cout << "Square::Draw()" << endl; }
    ~Square() { cout << "Square::~Square()" << endl; }
};

int main()
{
    vector<Shape*> vs; //元素为对象指针
    vs.push_back(new Circle);
    vs.push_back(new Square);
    for_each(vs.begin(), vs.end(), mem_fun(&Shape::draw));
    for(unsigned i=0;i<vs.size();i++)
        delete vs[i];
    return 0;
}

注意for_each只是通过函数对象执行每一个元素.
transform对应的函数对象不能返回void
实例代码2:

#include <algorithm>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
#include <ctime>
using namespace std;

class NumStringGen //随机生成一个string实数
{
    const int sz;
public:
    NumStringGen(int n=7):sz(n){}
    string operator()()
    {
        string digit("0123456789");
        string ret(sz,' ');
        ret[0]=digit[rand()%9+1];//第一位不为0
        for(int i=1;i<sz;i++)
        {
            if(sz>3&&i==sz/2) ret[i]='.';//中间插入'.'
            else ret[i]=digit[rand()%10];
        }
        return ret;
    }
};

int main()
{
    srand(time(0));
    const int N=10;
    vector<string> vecstr(N); //保存string类型
    const char* arrpc[N];//保存char*类型
    vector<double> vecdou;//保存double类型
    generate(vecstr.begin(),vecstr.end(),NumStringGen());
    //下面的使用
    transform(vecstr.begin(),vecstr.end(),arrpc,mem_fun_ref(&string::c_str));
    transform(arrpc,arrpc+N,back_inserter(vecdou),atof); //atof本身就是函数对象??

    ostream_iterator<double> out(cout," ");
    copy(vecdou.begin(),vecdou.end(),out);
    cout<<endl;
}