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書名： Microsoft Visual C++ Windows Applications by Example
作者名： Stefan Bjornander
本章字數： 173字
更新時間： 2021-07-02 12:02:24

Namespaces

Code can be placed in functions and functions can be placed in classes as methods. The next step is to create a namespace that contains classes, functions, and global variables.

namespace TestSpace
{
  double Square(double dValue);

  class BankAccount
  {
    public:
      BankAccount();
      double GetSaldo() const;

      void Deposit(double dAmount);
      void Withdraw(double dAmount);

    private:
      double m_dSaldo;
  };
};

double TestSpace::Square(double dValue)
{
  return dValue * dValue;    
}

TestSpace::BankAccount::BankAccount()
 :m_dSaldo(0)
{
  // Empty.
}
// ...

void main()
{
  int dSquare = TestSpace::Square(3.14);
  TestSpace::BankAccount account;
  account.Deposit(1000);
  account.Withdraw(500);
  double dSaldo = account.GetSaldo();
}

We could also choose to use the namespace. If so, we do not have to refer to the namespace explicitly. This is what we did with the std namespace at the beginning of Chapter 1.

#include <iostream>
using namespace std;

namespace TestSpace
{
  // ...
};

// ...

using namespace TestSpace;

void main()
{
  cout << square(3.14);
  BankAccount account;
  account.deposit(1000);
  account.withdraw(500);
  cout << account.getSaldo();
}

Finally, namespaces can be nested. A namespace may hold another namespace, which in turn can hold another namespace and so on.

#include <iostream>
using namespace std;

namespace Space1
{
  namespace Space2
  {
    double Square(double dValue);
  };
};


double Space1::Space2::Square(double dValue)
{
  return dValue * dValue;
}

void main(void)
{
  cout << Space1::Space2::Square(3);
}

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Microsoft Visual C++ Windows Applications by Example

Namespaces