Question

我正在尝试在C ++中实现策略模式，以使我的代码更灵活（并学习一些OO编程）。在main（）的第3行显示的动态强制转换失败。此外，我得到一些非常奇怪的错误消息。你能解释一下我做错了什么吗？我不习惯在C ++中使用设计模式。

我从编译器得到的错误消息：

/*
/tmp/cc8b482g.o: In function `individual::setObjectiveFunction(int)':
main.cpp:(.text+0x20b): undefined reference to `ObjectiveFunctionhyperBowl::ObjectiveFunctionhyperBowl()'
/tmp/cc8b482g.o: In function `main':
main.cpp:(.text+0x25e): undefined reference to `ObjectiveFunctionhyperBowl::ObjectiveFunctionhyperBowl()'
main.cpp:(.text+0x344): undefined reference to `ObjectiveFunctionhyperBowl::~ObjectiveFunctionhyperBowl()'
main.cpp:(.text+0x3ac): undefined reference to `ObjectiveFunctionhyperBowl::~ObjectiveFunctionhyperBowl()'
*/

编辑：“6502”中有一个正确的建议我在声明之前使用了一个类（这是整个代码的修剪版本）

ObjectiveFunctionhyperBowl的构造函数在那里，不是吗？

我错过了什么，声明现在就在它的使用位置上方，它仍然不起作用......

再次提前Thanx！

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#include <iostream>
#include <sstream>
#include <random>
#include <assert.h>
#include <vector>
class individual;
class objectiveFunctionStrategy;

/*
 * This is my abstract class implementation for a strategy.
 */
class objectiveFunctionStrategy
{
public:
    objectiveFunctionStrategy();
    virtual ~objectiveFunctionStrategy();
    virtual float evaluate(individual)=0;
};

/*
 * The class individual should contain strategy objects
 */
class individual{
    private:
        std::vector<float>                 featureVector;
        objectiveFunctionStrategy *        ofstrategy;
        unsigned int ndim;

    public:
        /*Constructors*/
        individual(std::vector<float>);
        float getObjectiveFunction();
        void setObjectiveFunction(int k);
        std::vector<float> getFeatureVector();
};

individual::individual(std::vector<float> fv){
    for(unsigned int i=0;i<fv.size() ; i++){
        featureVector.push_back(fv[i]);
    }
    this -> ndim = featureVector.size();
}

std::vector<float> individual::getFeatureVector(){
    return this->featureVector;
}

float individual::getObjectiveFunction(){
    /*
     *Here I'm planning of passing a concrete strategy object to 
     *make the objective functions interchangeable.
     * 
     *So the calculation would be ofstrategy.evaluate()
     */
    float Fc=0;
    if(false == false){
        std::vector<float> vv = this->featureVector;
        Fc = ofstrategy->evaluate(vv);
    }
    return Fc;
}

/*
 * Now this one is a concrete strategy object class:
 */
class ObjectiveFunctionhyperBowl: public objectiveFunctionStrategy
{
public:
    /*
     * could have a reference to the individual.
     * might do things a bit more complicated.
     */
    ObjectiveFunctionhyperBowl();    
    ~ObjectiveFunctionhyperBowl();

    float evaluate(individual ind){
        float Fc =0 ;
        std::vector<float> v = ind.getFeatureVector();
        for(unsigned int i=0;i<v.size();i++){
            Fc += v[i]*v[i];
        }
        return Fc;
    }
};

void individual::setObjectiveFunction(int i){
    /*
     * here the strategy is defined inside the class by an integer
     */
    this->ofstrategy = new ObjectiveFunctionhyperBowl;
}


int main(){
    std::vector<float> v;
    ObjectiveFunctionhyperBowl hb;
    objectiveFunctionStrategy* ofs;
    ofs = dynamic_cast<objectiveFunctionStrategy*> (&hb);
    individual indiv(v);
    /*
     * Now the above still does not compile...
     * error message:
     * 
     * 
     * 
     */
    v.push_back(2.1);
    v.push_back(22.1);
    hb.evaluate(indiv);
}

Answer 1

您的代码正在使用

new ObjectiveFunctionhyperBowl;

在声明课程ObjectiveFunctionhyperBowl之前;在这种情况下，C ++不进行预测，因此您必须在使用它之前声明该类。

在individual::setObjectiveFunction方法实现之前移动类声明应该足够了。一般来说，如果可能的话，最好在include .h文件中包含所有声明（和声明），并在.cpp单独文件中实现。

为什么我不能进行动态演员表演？ C中的战略模式

1 个答案: