错误C3861：找不到标识符

Question

我在这段代码中遇到了以下问题。

 #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>

//////////////////////////////////////////////////////////
//////////////////////////CORE CLASS//////////////////////
//////////////////////////////////////////////////////////
class Core {
public:
    Core() : midterm(0), final(0) { }
    Core(std::istream& is) { read(is); }

    std::string name() const;

    virtual std::istream& read(std::istream&);
    virtual double grade() const;
protected:
    std::istream& read_common(std::istream&);
    std::istream& read_hw(std::istream&, std::vector<double>&);
    double midterm, final;
    std::vector<double> homework;
private:    
    std::string n;  
};

std::string Core::name() const { return n; }

double Core::grade() const
{
    return calc_grade(midterm, final, homework);
}

std::istream& Core::read_common(std::istream& in)
{
    in >> n >> midterm >> final;
    return in;
}

std::istream& Core::read(std::istream& in)
{
    read_common(in);
    read_hw(in, homework);
    return in;
}

std::istream& Core::read_hw(std::istream& in, std::vector<double>& homework)
{
    double input;
    while (in >> input)
        homework.push_back(input);

    return in;
}

//////////////////////////////////////////////////////////
//////////////////////////GRAD CLASS//////////////////////
//////////////////////////////////////////////////////////
class Grad : public Core {
public:
    Grad() : thesis(0) { }
    Grad(std::istream& is) { read(is); }

    double grade() const;
    std::istream& read(std::istream&);
private:
    double thesis;
};

std::istream& Grad::read(std::istream& in)
{
    read_common(in);
    in >> thesis;
    read_hw(in, homework);
    return in;
}

double Grad::grade() const
{
    return std::min(Core::grade(), thesis);
}

//////////////////////////////////////////////////////////
//////////////////////MISCELLANEOUS///////////////////////
//////////////////////////////////////////////////////////
bool compare_grades(const Core& c1, const Core& c2)
{
    return c1.grade() < c2.grade();
}

bool compare_Core_ptrs(const Core* cp1, const Core* cp2)
{
    return compare_grades(*cp1, *cp2);
}

double calc_grade(double midterm, double final, std::vector<double>& homework)
{
    double result = 0.0;
    for (std::vector<double>::const_iterator i = homework.begin(); i != homework.end(); ++i)
        result += *i;

    return midterm*0.4 + final*0.4 + (result / homework.size())*0.2;
}

using namespace std;

int main()
{
    vector<Core*> students;
    Core* record;
    char ch;
    string::size_type maxlen = 0;

    while (cin >> ch)
    {
        if (ch == 'U')
            record = new Core;
        else
            record = new Grad;
        record->read(cin);
        maxlen = max(maxlen, record->name().size());
        students.push_back(record);
    }

    sort(students.begin(), students.end(), compare_Core_ptrs);

    for (vector<Core*>::size_type i = 0; i != students.size(); ++i)
    {
        cout << students[i]->name() << string(maxlen + 1 - students[i]->name().size(), ' ');
        try
        {
            double final_grade = students[i]->grade();
            streamsize prec = cout.precision();
            cout << setprecision(3) << final_grade << setprecision(prec) << endl;
        }
        catch (domain_error e)
        {
            cout << e.what() << endl;
        }
        delete students[i];
    }
    return 0;
}

错误C3861：＆＃39; calc_grade＆＃39;：找不到标识符。我尝试在类之前移动函数但没有任何改变。我不明白什么是错的。帮助

Answer 1

您需要将calc_grade移动到等级之上，以便它知道它存在。或者像上面这样声明它。

double calc_grade(double midterm, double final, std::vector<double>& homework);

您的成绩方法标记为常量，因此可能不会更改您的成绩。但是你正在调用calc_grade，它不会采用const向量，因为它可以改变你正在处理它的类成员。你可以使用const向量来解决这个问题。我也会把这个方法设为const以保持一致。

一种可能的解决办法：

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>

//////////////////////////////////////////////////////////
//////////////////////////CORE CLASS//////////////////////
//////////////////////////////////////////////////////////
class Core {
public:
    Core() : midterm(0), final(0) { }
    Core(std::istream& is) { read(is); }

    std::string name() const;

    virtual std::istream& read(std::istream&);
    virtual double grade() const;
protected:
    std::istream& read_common(std::istream&);
    std::istream& read_hw(std::istream&, std::vector<double>&);
    double midterm, final;
    std::vector<double> homework;
private:    
    std::string n;  
};

std::string Core::name() const { return n; }


double calc_grade(double midterm, double final, const std::vector<double>& homework)
{
    double result = 0.0;
    for (std::vector<double>::const_iterator i = homework.begin(); i != homework.end(); ++i)
        result += *i;

    return midterm*0.4 + final*0.4 + (result / homework.size())*0.2;
}


double Core::grade() const
{
    return calc_grade(midterm, final, homework);
}

std::istream& Core::read_common(std::istream& in)
{
    in >> n >> midterm >> final;
    return in;
}

std::istream& Core::read(std::istream& in)
{
    read_common(in);
    read_hw(in, homework);
    return in;
}

std::istream& Core::read_hw(std::istream& in, std::vector<double>& homework)
{
    double input;
    while (in >> input)
        homework.push_back(input);

    return in;
}

//////////////////////////////////////////////////////////
//////////////////////////GRAD CLASS//////////////////////
//////////////////////////////////////////////////////////
class Grad : public Core {
public:
    Grad() : thesis(0) { }
    Grad(std::istream& is) { read(is); }

    double grade() const;
    std::istream& read(std::istream&);
private:
    double thesis;
};

std::istream& Grad::read(std::istream& in)
{
    read_common(in);
    in >> thesis;
    read_hw(in, homework);
    return in;
}

double Grad::grade() const
{
    return std::min(Core::grade(), thesis);
}

//////////////////////////////////////////////////////////
//////////////////////MISCELLANEOUS///////////////////////
//////////////////////////////////////////////////////////
bool compare_grades(const Core& c1, const Core& c2)
{
    return c1.grade() < c2.grade();
}

bool compare_Core_ptrs(const Core* cp1, const Core* cp2)
{
    return compare_grades(*cp1, *cp2);
}

using namespace std;

int main()
{
    vector<Core*> students;
    Core* record;
    char ch;
    string::size_type maxlen = 0;

    while (cin >> ch)
    {
        if (ch == 'U')
            record = new Core;
        else
            record = new Grad;
        record->read(cin);
        maxlen = max(maxlen, record->name().size());
        students.push_back(record);
    }

    sort(students.begin(), students.end(), compare_Core_ptrs);

    for (vector<Core*>::size_type i = 0; i != students.size(); ++i)
    {
        cout << students[i]->name() << string(maxlen + 1 - students[i]->name().size(), ' ');
        try
        {
            double final_grade = students[i]->grade();
            streamsize prec = cout.precision();
            cout << setprecision(3) << final_grade << setprecision(prec) << endl;
        }
        catch (domain_error e)
        {
            cout << e.what() << endl;
        }
        delete students[i];
    }
    return 0;
}