{ "cells": [ { "cell_type": "markdown", "metadata": {}, "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", "execution_count": null, "metadata": {}, "outputs": [], "source": [ "#include \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 \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 \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 \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. . ." ] } ], "metadata": { "kernelspec": { "display_name": "Python 3.6.3", "language": "python", "name": "python3.6.3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.6.3" }, "toc": { "base_numbering": 1, "nav_menu": {}, "number_sections": false, "sideBar": true, "skip_h1_title": false, "title_cell": "Table of Contents", "title_sidebar": "Contents", "toc_cell": false, "toc_position": {}, "toc_section_display": true, "toc_window_display": true } }, "nbformat": 4, "nbformat_minor": 4 }