17_C++的内存模型.ipynb

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   "source": [
    "# C++的内存模型"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 1. 内存分区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① C++在程序执行时，将内存大方向划分为4个区域。\n",
    "\n",
    "1. 代码区：存放函数体的二进制代码，由操作系统进行管理的。\n",
    "2. 全局区：存放全局变量和静态变量以及常量。\n",
    "3. 栈区：由编译器自动分配释放，存放函数的参数值、局部变量等。\n",
    "4. 堆区：由程序员分配和释放，若程序员不释放，程序结束时由操作系统回收。\n",
    "\n",
    "② 内存四区的意义：不同区域存放的数据，赋予不同的生命周期，给我们更大的灵活编程。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 在程序编译后，生成了exe可执行程序，未执行该程序前分为两个区域：代码区、全局区。\n",
    "\n",
    "② 所有的写的代码(注释、变量、语句等)都会放到代码区中。\n",
    "\n",
    "③ 栈区中的数据由编译器决定数据的生成和死亡。\n",
    "\n",
    "④ 堆区中的数据由程序员决定数据的生存和死亡。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 2. 内存四区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.1 代码区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 代码区：\n",
    "\n",
    "1. 存放CPU执行的机器指令。\n",
    "2. 代码区是共享的，共享的目的是对于频繁被执行的程序，只需要内存中有一份代码即可。\n",
    "3. 代码区是只读的，使其只读的原因是防止程序员意外地修改了它的指令。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.2 全局区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 全局区：\n",
    "\n",
    "1. 全局变量和静态变量存放在此，局部常量不放在全局区。\n",
    "2. 全局区还包含了常量区，字符串常量和其他常量也存放在此。\n",
    "3. 该区域的数据在程序结束后由操作系统释放。"
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "#include <iostream>\n",
    "using namespace std;\n",
    "\n",
    "//全局变量\n",
    "int g_a = 10;\n",
    "int g_b = 20;\n",
    "\n",
    "//const修饰的全局常量\n",
    "const int c_g_a = 50;\n",
    "const int c_g_b = 60;\n",
    "\n",
    "int main()\n",
    "{\n",
    "    //全局区\n",
    "\n",
    "    //全局变量、静态变量、常量\n",
    "\n",
    "    //创建普通局部变量\n",
    "    int a = 30;\n",
    "    int b = 40;\n",
    "\n",
    "    cout << \"局部变量a的地址为：\" << (int)&a << endl;\n",
    "    cout << \"局部变量b的地址为：\" << (int)&b << endl;\n",
    "\n",
    "    cout << \"全局变量g_a的地址为：\" << (int)&g_a << endl;\n",
    "    cout << \"全局变量g_b的地址为：\" << (int)&g_b << endl;\n",
    "\n",
    "    //静态变量  在普通变量前面加static,属于静态变量\n",
    "    static int s_a = 10;\n",
    "    static int s_b = 10;\n",
    "\n",
    "    cout << \"静态变量s_a的地址为：\" << (int)&s_a << endl;\n",
    "    cout << \"静态变量s_b的地址为：\" << (int)&s_b << endl;\n",
    "\n",
    "    //常量\n",
    "    //字符串常量\n",
    "    cout << \"字符串常量的地址为：\" << (int)&\"hello world\" << endl;\n",
    "\n",
    "    //const修饰的变量\n",
    "    //const修饰的局部变量,const修饰的局部变量\n",
    "    cout << \"全局常量c_g_a的地址为：\" << (int)&c_g_a << endl;\n",
    "    cout << \"全局常量c_g_a的地址为：\" << (int)&c_g_b << endl;\n",
    "\n",
    "    const int c_l_a = 10;  // c-const g-global  l-local;\n",
    "    const int c_l_b = 10;\n",
    "    cout << \"局域常量c_l_a的地址为：\" << (int)&c_l_a << endl;\n",
    "    cout << \"局域常量c_l_b的地址为：\" << (int)&c_l_a << endl;\n",
    "\n",
    "    system(\"pause\");\n",
    "\n",
    "    return 0;\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果：  \n",
    " - 局部变量a的地址为：14023100  \n",
    " - 局部变量b的地址为：14023088  \n",
    " - 全局变量g_a的地址为：4964352  \n",
    " - 全局变量g_b的地址为：4964356  \n",
    " - 静态变量s_a的地址为：4964360  \n",
    " - 静态变量s_b的地址为：4964364  \n",
    " - 字符串常量的地址为：4955128  \n",
    " - 全局常量c_g_a的地址为：4954928  \n",
    " - 全局常量c_g_a的地址为：4954932  \n",
    " - 局域常量c_l_a的地址为：14023076  \n",
    " - 局域常量c_l_b的地址为：14023076  \n",
    " - 请按任意键继续. . ."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.3 栈区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 栈区\n",
    "\n",
    "1. 由编译器自动分配释放，存放函数的参数值、局部变量等。\n",
    "2. 不要返回局部变量的地址，栈区开辟的数据由编译器自动释放。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "#include <iostream>\n",
    "using namespace std;\n",
    "\n",
    "//栈区数据注意事项：不要返回局部变量的地址\n",
    "//栈区的数据由编译器管理开辟和释放\n",
    "\n",
    "int* func(int b)  //返回的是一个地址 int*；形参的数据也会放在栈区\n",
    "{\n",
    "    int a = 10;  //局部变量存放的数据10存放在栈区，栈区的数据在函数执行完后自动释放\n",
    "    return &a;   //返回局部变量的地址，即数据10的的地址\n",
    "}\n",
    "\n",
    "int main()\n",
    "{\n",
    "    //接收func函数的返回值\n",
    "    int* p = func(1);    //用指针接收栈区上的数据10的地址，由于栈区上数据10已经被释放，所以对地址解引用会获得乱码的值。\n",
    "\n",
    "    cout << *p << endl;  //第一次可以 打印正确的数字，是因为编译器做了保留\n",
    "    cout << *p << endl;  //第二次这个数据就不在保留了。\n",
    "\n",
    "    system(\"pause\");\n",
    "\n",
    "    return 0;\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果：  \n",
    " - 10  \n",
    " - 1905325  \n",
    " - 请按任意键继续. . ."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2.4 堆区"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① 堆区：\n",
    "\n",
    "1. 由程序员分配释放，若程序员不释放，程序结束时由操作系统回收。\n",
    "2. 在C++中主要利用new在堆区开辟内存。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "#include <iostream>\n",
    "using namespace std;\n",
    "\n",
    "int* func()  //返回的是一个地址 int*；形参的数据也会放在栈区\n",
    "{\n",
    "    //利用new关键字，可以将数据开辟到堆区\n",
    "    //指针本质也是变量，这里的指针是局部变量，局部变量的数据放在栈上，即指针保存的数据是放在堆区\n",
    "    int * p = new int(10);   //new关键字会返回一个地址，因此用栈上的指针来接收堆上数据的地址。\n",
    "    return p;\n",
    "}\n",
    "int main()\n",
    "{\n",
    "    //在堆区开辟数据\n",
    "    int* p = func(); //堆区的地址返回给 *p 了，栈区数据是否，堆区数据没释放\n",
    "\n",
    "    cout << *p << endl;\n",
    "    cout << *p << endl;\n",
    "    cout << *p << endl;\n",
    "    cout << *p << endl;\n",
    "\n",
    "    system(\"pause\");\n",
    "\n",
    "    return 0;\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果：  \n",
    " - 10  \n",
    " - 10  \n",
    " - 10  \n",
    " - 10  \n",
    " - 请按任意键继续. . ."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 3. new操作符"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "① C++中利用new操作符在堆区开辟数据。\n",
    "\n",
    "② 堆区开辟的数据，由程序员手动开辟，手动释放，释放利用操作符 delete。\n",
    "\n",
    "③ 语法：new 数据类型\n",
    "\n",
    "④ 利用new创建的数据，会返回该数据对应的类型的指针。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "#include <iostream>\n",
    "using namespace std;\n",
    "\n",
    "//1、new的基本语法\n",
    "\n",
    "int* func()  //返回的是一个地址 int*；形参的数据也会放在栈区\n",
    "{\n",
    "    //在堆区创建整型数据\n",
    "    //new返回是该数据类型的指针\n",
    "    int* p = new int(10);\n",
    "    return p;\n",
    "}\n",
    "\n",
    "void test01()\n",
    "{\n",
    "    int* p = func();\n",
    "    cout << *p << endl;\n",
    "    cout << *p << endl;\n",
    "    cout << *p << endl;\n",
    "    //堆区的数据，由程序员管理开辟，程序员管理释放\n",
    "    //如果想释放堆区数据，利用关键字 delete\n",
    "    delete p;\n",
    "\n",
    "    // cout << *p << endl;  //报错，内存已经被释放，再次访问就是非法操作，会报错\n",
    "}\n",
    "\n",
    "//2、在堆区利用new开辟数据\n",
    "void test02()\n",
    "{\n",
    "    //创建10整型数据的数组，在堆区\n",
    "    int* arr = new int[10];//10代表数组有10个元素\n",
    "\n",
    "    for (int i = 0; i < 10; i++)\n",
    "    {\n",
    "        arr[i] = i + 100; //给10个元素赋值 100~109\n",
    "    }\n",
    "\n",
    "    for (int i = 0; i < 10; i++)\n",
    "    {\n",
    "        cout << arr[i] << endl; \n",
    "    }\n",
    "    //释放堆区数据\n",
    "    //释放数组的时候，要加[]才可以\n",
    "    delete[] arr;\n",
    "}\n",
    "\n",
    "int main()\n",
    "{\n",
    "    test01();\n",
    "    test02();\n",
    "\n",
    "    system(\"pause\");\n",
    "\n",
    "    return 0;\n",
    "\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行结果：  \n",
    " - 10  \n",
    " - 10  \n",
    " - 10  \n",
    " - 100  \n",
    " - 101  \n",
    " - 102  \n",
    " - 103  \n",
    " - 104  \n",
    " - 105  \n",
    " - 106  \n",
    " - 107  \n",
    " - 108  \n",
    " - 109  \n",
    " - 请按任意键继续. . ."
   ]
  }
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