從成員函數調用構造函數
[英]calling constructor from member function
問題描述
這是問題：
定義一個名為Month的類，該類是一個月的抽象數據類型。 您的班級將有一個類型為int的成員變量來表示一個月（1表示1月，2表示2月，依此類推）。 包括以下所有成員函數：構造函數，使用月份名稱中的前三個字母作為三個參數設置月份；構造函數，使用整數作為參數設置月份（1表示1月，2表示2月，依此類推），默認構造函數，將月份作為整數讀取的輸入函數，將月份作為月份名稱中的前三個字母讀取的輸入函數，將月份作為整數輸出的輸出函數，輸出函數，輸出月作為月名稱中的前三個字母，成員函數返回下個月作為月類型的值。 將類定義嵌入測試程序中。
#include <iostream>
using namespace std;
class Month
{
public:
Month (char letter1, char letter2, char letter3);
Month (int numOfMonth);
Month ();
void inputAsNum(); // read month as integer
void inputAsCh(); // read first three chars of month
void outputAsCh() const;
void outputAsNum() const;
Month nextMonth();
private:
int month;
};
int main()
{
Month test(5);
//test.inputAsNum();
cout << "Current month is " << endl;
test.outputAsCh();
test.outputAsNum();
cout << endl;
test.nextMonth();
cout << "Next month is " <<endl;
test.outputAsCh();
test.outputAsNum();
cout << endl;
Month test2('a','p','r');
//test2.inputAsCh();
cout << "Current month is " << endl;
test2.outputAsCh();
test2.outputAsNum();
cout << endl;
test2.nextMonth();
cout << "Next month is " <<endl;
test2.outputAsCh();
test2.outputAsNum();
cout << endl;
Month test3;
test3.inputAsNum();
cout << "Current month is " << endl;
test3.outputAsCh();
test3.outputAsNum();
cout << endl;
test3.nextMonth();
cout << "Next month is " <<endl;
test3.outputAsCh();
test3.outputAsNum();
cout << endl;
Month test4;
test4.inputAsCh();
cout << "Current month is " << endl;
test4.outputAsCh();
test4.outputAsNum();
cout << endl;
test4.nextMonth();
cout << "Next month is " <<endl;
test4.outputAsCh();
test4.outputAsNum();
cout << endl;
return 0;
}
Month::Month (char letter1, char letter2, char letter3)
{
if ((letter1 == 'j')&&(letter2 == 'a')&&(letter3 == 'n'))
month= 1;
else if ((letter1 == 'f')&&(letter2 == 'e')&&(letter3 == 'b'))
month= 2;
else if ((letter1 == 'm')&&(letter2 == 'a')&&(letter3 == 'r'))
month= 3;
else if ((letter1 = 'a')&&(letter2 == 'p')&&(letter3 == 'r'))
month= 4;
else if ((letter1 == 'm')&&(letter2 == 'a')&&(letter3 == 'y'))
month= 5;
else if ((letter1 == 'j')&&(letter2 == 'u')&&(letter3 == 'n'))
month= 6;
else if ((letter1 == 'j')&&(letter2 == 'u')&&(letter3 == 'l'))
month= 7;
else if ((letter1 == 'a')&&(letter2 == 'u')&&(letter3 == 'g'))
month= 8;
else if ((letter1 == 's')&&(letter2 == 'e')&&(letter3 == 'p'))
month= 9;
else if ((letter1 == 'o')&&(letter2 == 'c')&&(letter3 == 't'))
month= 10;
else if ((letter1 == 'n')&&(letter2 == 'o')&&(letter3 == 'v'))
month= 11;
else if ((letter1 == 'd')&&(letter2 == 'e')&&(letter3 == 'c'))
month= 12;
}
Month::Month (int numOfMonth)
:month(numOfMonth)
{ }
Month::Month ()
:month(1)
{ }
void Month::inputAsNum()
{
int num;
cout << "Enter num of month => ";
cin >> num;
month = num;
}
void Month::inputAsCh()
{
char c1,c2,c3;
cout << "Enter three letters of month => ";
cin >> c1 >> c2 >> c3;
Month::Month(c1,c2,c3);
}
void Month::outputAsCh() const
{
if (month == 1)
cout << "Jan ";
else if (month == 2)
cout << "Feb ";
else if (month == 3)
cout << "Mar ";
else if (month == 4)
cout << "Apr ";
else if (month == 5)
cout << "May ";
else if (month == 6)
cout << "Jun ";
else if (month == 7)
cout << "Jul ";
else if (month == 8)
cout << "Aug ";
else if (month == 9)
cout << "Sep ";
else if (month == 10)
cout << "Oct ";
else if (month == 11)
cout << "Nov ";
else if (month == 12)
cout << "Dec ";
}
void Month::outputAsNum() const
{
cout << month;
}
Month Month::nextMonth()
{
if (month < 12)
month++;
else if (month == 12)
month = 1;
return Month(month);
}
代碼運行正常。 我嘗試從成員函數void Month::inputAsCh()調用構造函數Month::Month (char letter1, char letter2, char letter3) void Month::inputAsCh() 。 我可以通過更改Month::inputAsCh()定義並將復制構造函數的粘貼定義復制到函數中來解決該問題。 但是，出於好奇，可以從成員函數中調用構造函數嗎？ 如果沒問題，那么Month::inputAsCh()出錯，我也嘗試使用Month test4變量。
Output Expected Output
------------- -----------------
Current month is Current month is
Nov 11 Nov 11
Next month is Next month is
Dec 12 Dec 12
Current month is Current month is
Apr 4 Apr 4
Next month is Next month is
May 5 May 5
Enter num of month => 2 Enter num of month => 2
Current month is Current month is
Feb 2 Feb 2
Next month is Next month is
Mar 3 Mar 3
Enter three letters of month => apr Enter three letters of month => apr
Current month is Current month is
Jan 1 Apr 4
Next month is Next month is
Feb 2 May 5
1 個解決方案
解決方案1
2 已采納 2015-08-14 08:04:39
Month::Month(c1,c2,c3);
該行不會更新當前對象。 這應該是錯誤的，因為Month::Month在該上下文中命名了構造函數，但是某些編譯器（尤其是clang ）會將其解釋為臨時對象的構造（這要感謝user657267進行更正）。
您可以將月份計算代碼分解為一個單獨的函數，然后從構造函數和inputAsCh函數中調用該函數：
void setMonth(char letter1, char letter2, char letter3)
{
if ((letter1 == 'j')&&(letter2 == 'a')&&(letter3 == 'n'))
month= 1;
else if ((letter1 == 'f')&&(letter2 == 'e')&&(letter3 == 'b'))
month= 2;
else if ((letter1 == 'm')&&(letter2 == 'a')&&(letter3 == 'r'))
month= 3;
else if ((letter1 = 'a')&&(letter2 == 'p')&&(letter3 == 'r'))
month= 4;
else if ((letter1 == 'm')&&(letter2 == 'a')&&(letter3 == 'y'))
month= 5;
else if ((letter1 == 'j')&&(letter2 == 'u')&&(letter3 == 'n'))
month= 6;
else if ((letter1 == 'j')&&(letter2 == 'u')&&(letter3 == 'l'))
month= 7;
else if ((letter1 == 'a')&&(letter2 == 'u')&&(letter3 == 'g'))
month= 8;
else if ((letter1 == 's')&&(letter2 == 'e')&&(letter3 == 'p'))
month= 9;
else if ((letter1 == 'o')&&(letter2 == 'c')&&(letter3 == 't'))
month= 10;
else if ((letter1 == 'n')&&(letter2 == 'o')&&(letter3 == 'v'))
month= 11;
else if ((letter1 == 'd')&&(letter2 == 'e')&&(letter3 == 'c'))
month= 12;
}
Month::Month (char letter1, char letter2, char letter3)
{
setMonth(letter1, letter2, letter3);
}
void Month::inputAsCh()
{
char c1,c2,c3;
cout << "Enter three letters of month => ";
cin >> c1 >> c2 >> c3;
setMonth(c1,c2,c3);
}
順便說一句，可以通過從這些char創建一個std::string並將其與之比較來大大簡化setMonth函數。
使用指向成員 function 的指針在另一個 class 中調用 class 構造函數
[英]Calling class constructor inside another class using a pointer to a member function
C++:: 在構造函數退出前通過指針調用成員 function
[英]C++ :: Calling Member function via pointer before constructor exit
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