在代碼（頭文件和實現文件）中放置#includes和Redundancies的位置

Question

我目前正在使用Accelerated C ++，我在理解哪些地方需要放入#include（無論是在頭文件和/或源文件中）還有一點困難，而且大多數情況下，我是否多余。

我很感激所有關於我應該改變什么以及什么是不必要的評論。 我覺得我多次包含庫（例如，如果主程序有#include，我是否需要在任何其他頭文件/源文件中使用它？）。 另外，如果使用

#include "Student_info.h" 

並且Student_info.cpp文件包含grade.h，我還需要在main.cpp中包含grade.h還是這樣就足夠了？ 我發布了這段代碼，因為我覺得應用到一個特定的例子是最好的方法來鑽研我組織這些文件的正確方法以及我應該注意的常見錯誤

文件清單 - 我將完整的代碼包括在內，但只有最重要的部分和原則才真正重要

main.cpp中

#include<iostream>
#include<string>
#include<ios>
#include<stdexcept>
#include<vector>
#include<algorithm>
#include<iomanip>
#include "grade.h"
#include "Student_info.h"
#include "analysis.h"



using std::cin;           using std::setprecision;
using std::cout;          using std::sort;
using std::domain_error;  using std::streamsize;
using std::endl;          using std::string;
using std::max;           using std::vector;

int main()
{
    //students who did and didn't do their homework
    vector<Student_info> did, didnt;

    //read the student records and partition them
    Student_info student;
    while (read(cin,student))
    {
        if (did_all_hw(student))
            did.push_back(student);
        else
            didnt.push_back(student);

    }

    //verify that the analyses will show us something
    if (did.empty())
    {
        cout<<"No student did all the homework!"<<endl;
        return 1;

    }
    if (didnt.empty())
    {
        cout<<"Every student did all the homework!"<<endl;
        return 1;
    }

    //do the analyses
    write_analysis(cout, "median",median_analysis, did, didnt);
    write_analysis(cout, "average",average_analysis, did, didnt);
    write_analysis(cout, "median of homework turned in", optimistic_median_analysis, did, didnt);

    return 0;
}

grade.h

#ifndef GUARD_grade_h
#define GUARD_grade_h

//grade.h - Header file
#include<vector>
#include "Student_info.h"


double grade(double, double, double);
double grade(double, double, const std::vector<double>&);
double grade(const Student_info&);

bool fgrade(const Student_info& s);
bool pgrade(const Student_info& s);

double grade_aux(const Student_info& s);

double average(const std::vector<double>& v);
double average_grade(const Student_info& s);
double optimistic_median(const Student_info& s);

#endif

grade.cpp

#include<stdexcept>
#include<vector>
#include<numeric>
#include "grade.h"
#include "median.h"
#include "Student_info.h"

using std::domain_error;
using std::vector;


//reference to constant vector of type double
//vector<double> homework
//vector<double>& hw = homework; (this means that hw is a synonym for homework)
//This function is a ALSO called grade
//This is OVERLOADING and the argument list will be checked to decide which function to call
//The & asks the implementation NOT to copy its argument and const means don't change it
double grade(double midterm, double final, const vector<double>& hw)
{
    if (hw.size()==0)
        throw domain_error("student has done no homework");
    return grade(midterm,final,median(hw));

}

double grade(double midterm, double final, double homework)
{
    return 0.2*midterm+0.4*final+0.4*homework;
}


//because it's a reference variable, there is no overboard in copying the object
//and modifying it in the function modifies the original variable passed in
//returns double representing OVERALL GRADE
double grade(const Student_info& s)
{
    return grade(s.midterm,s.final,s.homework);
}

bool fgrade(const Student_info& s)
{
    return grade(s) < 60;
}

bool pgrade(const Student_info& s)
{
    return !fgrade(s);
}

//need this function because the transform function can't use grade as there are too many overloaded versions
//and it doesn't know which one to call
double grade_aux(const Student_info& s)
{
    try {
        return grade(s);
    }
    catch (domain_error)
    {
        return grade(s.midterm, s.final, 0);
    }
}

//Write the average function to use for average_analysis
double average(const vector<double>& v)
{
    //accumulate is defined in the <numeric> library
    //The accumulate function adds the values in range denoted by the first two arguments, starting with the
    //the value given by the third argument (which also gives the resulting type, e.g. 0.0 will make accumulate return a double
    return accumulate(v.begin(),v.end(),0.0)/v.size();
}

double average_grade(const Student_info& s)
{
    return grade(s.midterm,s.final, average(s.homework));
}


double optimistic_median(const Student_info& s)
{
    vector<double> nonzero;
    //extracts nonzero vectors from the homework vector and appends them to  (vector<double> nonzero)
    remove_copy(s.homework.begin(), s.homework.end(),
                back_inserter(nonzero),0);

    if (nonzero.empty())
        return grade(s.midterm,s.final,0);
    else
        return grade(s.midterm, s.final,median(nonzero));
}

analysis.h

#ifndef GUARD_output_analysis
#define GUARD_output_analysis
//output_analysis.h - header file
#include<iostream>
#include<vector>
#include<iterator>
#include "Student_info.h"
#include "grade.h"
#include "median.h"


using std::ostream; using std::string;



void write_analysis(ostream& out,
                    const string& name,
                    double analysis(const vector<Student_info>&),
                    const vector<Student_info>& did,
                    const vector<Student_info>& didnt);


double median_analysis(const vector<Student_info>& students);
double average_analysis(const vector<Student_info>& students);
double optimistic_median_analysis(const vector<Student_info>& students);



#endif

analysis.cpp

#include<iterator>
#include<algorithm>
#include "Student_info.h"
#include "grade.h"
#include "median.h"

using std::istream; using std::vector;
using std::ostream; using std::string;
using std::endl;    using std::transform;


void write_analysis(ostream& out,
                    const string& name,
                    double analysis(const vector<Student_info>&),
                    const vector<Student_info>& did,
                    const vector<Student_info>& didnt)
{
    out <<name <<" : median(did) = "<<analysis(did)
        <<", median(didnt) = "<<analysis(didnt)<<endl;

}

double median_analysis(const vector<Student_info>& students)
{
    vector<double> grades;

    //The function grade is applied to every element in the range students.begin() to students.end()
    //and this is appended to the end of the grades vector
    transform(students.begin(), students.end(), back_inserter(grades), grade_aux);

    return median(grades);
}

double average_analysis(const vector<Student_info>& students)
{
    vector<double> grades;

    //recall that tranform applies the average_grade function to every element between students.begin() and students.end()
    //and appends this to the end of the grade vector (which is where the iterator returned by back_inserter(grades) points to
    transform(students.begin(), students.end(),
              back_inserter(grades), average_grade);

    return median(grades);
}

double optimistic_median_analysis(const vector<Student_info>& students)
{
    vector<double> grades;

    transform(students.begin(),students.end(), back_inserter(grades),optimistic_median);

    return median(grades);

}

median.h

#ifndef GUARD_median_h
#define GUARD_median_h

//median.h
#include<vector>
double median(std::vector<double>);

#endif

median.cpp

#include "median.h"

using std::vector;
using std::sort;
using std::domain_error;

double median(vector<double> vec)
{
    typedef vector<double>::size_type vec_sz;

    vec_sz size=vec.size();

    //if the vector is empty, an exception is thrown
    //execution stops and passes to another part of the program
    //along with the exception object
    if (size==0)
        throw domain_error("median of an empty vector");

    sort(vec.begin(),vec.end());

    vec_sz mid = size/2;
    return size%2==0 ? ((vec[mid]+vec[mid-1])/2) : (vec[mid]);

}

Student_info.h

#ifndef GUARD_Student_info
#define GUARD_Student_info

//Student_info.h header file

#include<iostream>
#include<string>
#include<vector>

using std::vector;


struct Student_info {
    std::string name;
    double midterm,final;
    std::vector<double> homework;
};

bool compare(const Student_info&, const Student_info&);
bool did_all_hw(const Student_info& s);

bool pgrade(const Student_info& s);
std::istream& read(std::istream&, Student_info&);
std::istream& read_hw(std::istream&, std::vector<double>&);

vector<Student_info> extract_fails(vector<Student_info>& students);


#endif

Student_info.cpp

//Source file for Student_info related functions
#include "Student_info.h"
#include "grade.h"

using std::istream; using std::vector;

bool compare(const Student_info& x, const Student_info& y)
{
    return x.name < y.name;
}

istream& read(istream& is, Student_info& s)
{
    //read and store the student's name and midterm and final exam grades
    is >> s.name >> s.midterm >> s.final;

    read_hw(is, s.homework); //read AND store all the student's homework grades
    return is;

}

istream& read_hw(istream& in, vector<double>& hw)
{
    if (in) {

        //remove previous contents and leaves us with an empty vector
        hw.clear();

        double x;
        while (in>>x)
            hw.push_back(x);

        //clear the stream so that input will work for the next student
        //reset any error indicatiosn so that input can continue
        in.clear();
    }

    //this means we were given an object that we're NOT going to a copy and we will
    //return the object without copying it

    return in;
}


bool did_all_hw(const Student_info& s)
{
    //recall  that if 0 is not found in the sequence given by the first two iterators, then the 2nd argument is returned
    return ((find(s.homework.begin(), s.homework.end(), 0)) == s.homework.end());

}

//ONE-PASS SOLUTION
vector<Student_info> extract_fails(vector<Student_info>& students)
{
    vector<Student_info>::iterator iter=stable_partition(students.begin(),students.end(),pgrade);
    vector<Student_info> fail(iter,students.end()); //vector consisting of all failing elements

    students.erase(iter,students.end());
    return fail;
}

Answer 1

如果編譯器需要知道您正在使用的類型的大小，或者您是否嘗試訪問其中任何成員或方法（包括您未明確創建的方法，例如默認值），則只需要包含頭文件構造函數，析構函數或賦值運算符）。 在Grade.h您不需要#include "Student_info.h"因為Student_info是一個引用。 您可以使用前向聲明：

class Student_info; // Don't #include it, forward declare it

此外，您很少需要編寫標頭保護程序，因為所有現代編譯器都支持#pragma once ，在編譯期間只包含該文件一次。