1、在C++中,內存分成5個區,他們分別是堆、棧、自由存儲區、全局/靜態存儲區和常量存儲區。
棧:在執行函數時,函數內局部變量的存儲單元都可以在棧上創建,函數執行結束時這些存儲單元自動被釋放。棧內存分配運算內置於處理器的指令集中,效率很高,但是分配的內存容量有限。
堆:就是那些由new分配的內存塊,他們的釋放編譯器不去管,由我們的應用程序去控制,一般一個new就要對應一個delete。如果程序員沒有釋放掉,那麼在程序結束後,操作系統會自動回收。
自由存儲區:就是那些由malloc等分配的內存塊,他和堆是十分相似的,不過它是用free來結束自己的生命的。
全局/靜態存儲區:全局變量和靜態變量被分配到同一塊內存中,在以前的C語言中,全局變量又分爲初始化的和未初始化的,在C++裏面沒有這個區分了,他們共同佔用同一塊內存區。
常量存儲區:這是一塊比較特殊的存儲區,他們裏面存放的是常量,不允許修改。
2、C++中考慮內存佈局,主要是針對類內部的內存分佈。類的內存分佈涉及的內容比較多,我們先從最簡單的來看。
一、一個簡單的類,沒有繼承,沒有虛函數表
#include <iostream>
using namespace std;
class CBase
{
//public
public:
CBase()
{
}
};
class CBaseClass
{
//private members
private:
int nCount;
//public members
public:
//private member funcs
private:
CBaseClass(const CBaseClass &base)
{
}
CBaseClass &operator = (const CBaseClass& base)
{
return *this;
}
//public members
public:
CBaseClass(int count = 0)
{
nCount = count;
}
~CBaseClass()
{
}
};
void main()
{
CBase base;
cout << "base Size" << sizeof(base) << endl;
CBaseClass baseClass(10);
cout << "baseClass Size" << sizeof(baseClass) << endl;
cin.get();
}
上面代碼的輸出如下所示:
#include <iostream>
using namespace std;
class CBase
{
//public
public:
CBase()
{
}
};
class CBaseClass
{
//private members
private:
int nCount;
//public members
public:
//private member funcs
private:
CBaseClass(const CBaseClass &base)
{
}
CBaseClass &operator = (const CBaseClass& base)
{
return *this;
}
//public members
public:
CBaseClass(int count = 0)
{
nCount = count;
}
~CBaseClass()
{
}
};
class CDerivedClass : public CBaseClass
{
//private members:
private:
int nDeriveCount;
//public members
public:
int nCurrentNum;
//private member funcs
private:
CDerivedClass(const CDerivedClass& derived)
{
}
CDerivedClass & operator = (const CDerivedClass &derived)
{
return *this;
}
//public member funcs
public:
CDerivedClass(int nDerived = 0)
{
nDeriveCount = nDerived;
nCurrentNum = 0;
}
};
void main()
{
CBase base;
cout << "base Size:" << sizeof(base) << endl;
CBaseClass baseClass(10);
cout << "baseClass Size:" << sizeof(baseClass) << endl;
CDerivedClass derivedClass(12);
cout << "derivedClass Size:" << sizeof(derivedClass) << endl;
cin.get();
}
代碼輸出的內容如下:
#include <iostream>
using namespace std;
class CBase
{
//public
public:
CBase()
{
}
};
class CBaseClass
{
//private members
private:
int nCount;
//public members
public:
//private member funcs
private:
CBaseClass(const CBaseClass &base)
{
}
CBaseClass &operator = (const CBaseClass& base)
{
return *this;
}
//public members
public:
CBaseClass(int count = 0)
{
nCount = count;
}
~CBaseClass()
{
}
};
class CBaseClassNew
{
//private members
private:
int nCount;
//public members
public:
int nNewCount;
//private member funcs
private:
CBaseClassNew(const CBaseClassNew &base)
{
}
CBaseClassNew &operator = (const CBaseClassNew& base)
{
return *this;
}
//public members
public:
CBaseClassNew(int count = 0)
{
nCount = count;
}
~CBaseClassNew()
{
}
};
class CDerivedClass : public CBaseClass
{
//private members:
private:
int nDeriveCount;
//public members
public:
int nCurrentNum;
//private member funcs
private:
CDerivedClass(const CDerivedClass& derived)
{
}
CDerivedClass & operator = (const CDerivedClass &derived)
{
return *this;
}
//public member funcs
public:
CDerivedClass(int nDerived = 0)
{
nDeriveCount = nDerived;
nCurrentNum = 0;
}
};
class CMultiDerivedClass :public CDerivedClass, public CBaseClassNew
{
//private members
private:
int nMultiCount;
//public members
public:
int nNewMultiCount;
//private member funcs
private:
CMultiDerivedClass(const CMultiDerivedClass& derived)
{
}
CMultiDerivedClass & operator = (const CMultiDerivedClass &derived)
{
return *this;
}
//public member funcs
public:
CMultiDerivedClass(int nCount)
{
nMultiCount = nCount;
nNewMultiCount = 0;
}
~CMultiDerivedClass()
{
}
};
void main()
{
CBase base;
cout << "base Size:" << sizeof(base) << endl;
CBaseClass baseClass(10);
cout << "baseClass Size:" << sizeof(baseClass) << endl;
CDerivedClass derivedClass(12);
cout << "derivedClass Size:" << sizeof(derivedClass) << endl;
CMultiDerivedClass multiDerivedClass(5);
cout << "multiDerivedClass Size:" << sizeof(multiDerivedClass) << endl;
cin.get();
}
上面代碼的輸出如下: