c++ - 在 C++ 中将错误的值传递给构造函数

Question

我一直在到处搜索，但我找不到解决方案，尽管它可能是一个简单的解决方案，因为我刚刚开始。基本上，我试图通过构造函数传入两个值，但我传入的值在运行或调试时都不正确。

事务.h

#include <string>

class Transaction {
  private:
    int amount;
    std::string type; 

  public:
    Transaction(int amt, std::string kind);
    std::string Report() const;

    // ...irrelevant code...
};

事务.cpp

#include "Transaction.h"
using namespace std;

Transaction::Transaction(int amt, std::string kind) { };

string Transaction::Report() const {
  string report;
  report += " ";
  report += type;  // supposed to concat "Deposit" to string
  report += " ";
  report += to_string(amount);  // supposed to concat amount to string

  return report;
  // This doesn't return the word "Deposit", nor does
  // it return the correct amount. I don't think that
  // this is adding "Deposit" to 50, because the values
  // change every time I run the program.
}

参数.cpp

#include "Transaction.h"
#include <iostream>
using namespace std;

// ...irrelevant code...

int main() {

  int money = 50;
  cout << "Depositing $" << money << endl;

  Transaction deposit(money, "Deposit");  
  // For some reason, this doesn't pass in int money.

  cout << "Original: " << deposit.Report() << endl;
  // And this cout prints some large value instead of 50.

  // ...irrelevant code...
}

无论我做什么，值(value)都会改变。我得到的一些输出:

Depositing $50
Original:   13961048
After pass by value:   13961048
After pass by reference:   27922096

Depositing $50
Original:   11208536
After pass by value:   11208536
After pass by reference:   22417072

Depositing $50
Original:   14092120
After pass by value:   14092120
After pass by reference:   28184240

任何帮助我指明正确方向(或直接回答)的人都会很棒!

Answer 1

值正在传递给构造函数，好的。问题是您没有对它们做任何事情!

查看构造函数的实现:

Transaction::Transaction(int amt, std::string kind) { };

这没有做任何事情。特别是，它不会保存(存储)传递的参数值。

你可能想要这个:

Transaction::Transaction(int amt, std::string kind)
   : amount(amt)
   , type(kind)
{ }

奇怪的冒号语法被称为 member initialization list , 并如其所愿。

请注意，您应该已经能够在调试器中看到它。您要做的是在构造函数的定义上设置一个断点，然后检查参数的值是什么。您会看到它们被正确传递(并且值不是“错误的”)。然后你必须弄清楚为什么他们没有被保存，你可以通过从那时起单步执行代码很容易地看到这一点。