[英]Accessing class method for object from within another class, C++
我正在研究google c ++課程數據庫項目,並且陷入了困境。 我有兩個類用於創建作曲家對象的Composer和Database和一個用於存儲作曲家數組的數據庫對象。這些類在.h文件中定義,以包含在最終的.cpp文件中。 同時,我正在通過每個類的test.cpp文件來完成每個類的測試。 我的composer類似乎正在按預期工作,但是當我在數據庫中創建composer對象時,我的數據庫類無法從composer類訪問方法。 任何幫助是極大的贊賞。 文件如下。
作曲家課:
#include <iostream>
using namespace std;
const int kDefaultRanking = 10;
class Composer {
public:
Composer(): first_name_(), last_name_(), composer_yob_(), composer_genre_(),
ranking_(kDefaultRanking), fact_(){}
void set_first_name(string in_first_name){
first_name_ = in_first_name;
}
void set_last_name(string in_last_name){
last_name_ = in_last_name;
}
string get_last_name(){
return last_name_;
}
void set_composer_yob(int in_composer_yob){
composer_yob_ = in_composer_yob;
}
void set_composer_genre(string in_composer_genre){
composer_genre_ = in_composer_genre;
}
void set_ranking(int in_ranking){
ranking_ = in_ranking;
}
void set_fact(string in_fact){
fact_ = in_fact;
}
void Promote(int increment){
ranking_ -= increment;
}
void Demote(int decrement){
ranking_ += decrement;
}
void Display(){
cout << "First Name: " << first_name_ << endl;
cout << "Last Name: " << last_name_ << endl;
cout << "Year of Birth: " << composer_yob_ << endl;
cout << "Genre: " << composer_genre_ << endl;
cout << "Fact: " << fact_ << endl;
cout << "Ranking: " << ranking_ << endl;
}
private:
string first_name_;
string last_name_;
int composer_yob_; // year of birth
string composer_genre_; // baroque, classical, romantic, etc.
string fact_;
int ranking_;
};
作曲家測試:
#include <iostream>
#include "Composer.h"
using namespace std;
int main()
{
cout << endl << "Testing the Composer class." << endl << endl;
Composer composer;
composer.set_first_name("Ludwig van");
composer.set_last_name("Beethoven");
composer.set_composer_yob(1770);
composer.set_composer_genre("Romantic");
composer.set_fact("Beethoven was completely deaf during the latter part of
his life - he never heard a performance of his 9th symphony.");
composer.Promote(2);
composer.Demote(1);
composer.Display();
}
數據庫類:
#include <iostream>
#include "Composer.h"
const int kMaxComposers = 100;
class Database {
public:
Database(): composers_(), next_slot_(0){}
Composer& AddComposer(string in_first_name, string in_last_name,
string in_genre, int in_yob, string in_fact){
Composer composer;
composers_[next_slot_] = composer;
composer.set_first_name(in_first_name);
composer.set_last_name(in_last_name);
composer.set_composer_genre(in_genre);
composer.set_composer_yob(in_yob);
composer.set_fact(in_fact);
next_slot_++;
}
Composer& GetComposer(string in_last_name){
for(int i=0;i<kMaxComposers;i++){
if (composers_[i].get_last_name() == in_last_name){
composers_[i].Display();
}
}
}
void DisplayAll(){
for(int i=0;i<kMaxComposers;i++){
if(composers_[i].get_last_name().length() > 0){
composers_[i].Display();
}
}
};
void DisplayByRank();
private:
Composer composers_[kMaxComposers];
int next_slot_;
};
數據庫測試:
#include <iostream>
#include "Database.h"
using namespace std;
int main() {
Database myDB;
Composer& comp1 = myDB.AddComposer("Ludwig van", "Beethoven", "Romantic", 1770,
"Beethoven was completely deaf during the latter part of his life - he never
heard a performance of his 9th symphony.");
comp1.Promote(7);
Composer& comp2 = myDB.AddComposer("Johann Sebastian", "Bach", "Baroque", 1685,
"Bach had 20 children, several of whom became famous musicians as well.");
comp2.Promote(5);
Composer& comp3 = myDB.AddComposer("Wolfgang Amadeus", "Mozart", "Classical", 1756,
"Mozart feared for his life during his last year - there is some evidence
that he was poisoned.");
comp3.Promote(2);
cout << endl << "all Composers: " << endl << endl;
myDB.DisplayAll();
}
當編譯並運行testdatabase.cpp時,我獲得了composer類的正確顯示輸出,但是當測試調用comp1.promote(#)時,什么也沒有發生,並且排名顯示為每個Composer 10。
代替
Composer& AddComposer(string in_first_name, string in_last_name,
string in_genre, int in_yob, string in_fact){
Composer composer;
composers_[next_slot_] = composer;
嘗試
Composer& AddComposer(string in_first_name, string in_last_name,
string in_genre, int in_yob, string in_fact){
Composer &composer = composers_[next_slot_];
為何起作用=>這是C ++,而不是C#,您沒有引用composers [x],而是復制了(此刻)空Composer的內容。
開設朋友班可能會有幫助。
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