# 编程实例
#### 实例描述
本实例实现了在Huawei LiteOS上运行C++的代码。
1. 编写C++代码。
2. 在运行C++代码之前，先在app_init函数里以NO_SCATTER参数调用LOS_CppSystemInit初始化C++构造函数。
3. 在LOS_CppSystemInit之后调用编写好的C++代码。
 
#### 编程示例
前提条件：通过make menuconfig使能C++支持。
C++代码实现如下：
```
#ifdef __cplusplus
#if __cplusplus
extern "C" {
#endif /* __cplusplus */
#endif /* __cplusplus */
using namespace std;
class TestClass {
public:
    TestClass(int arg);
    ~TestClass(void);
    void PrintTest(void);
    void StringTest(void);
    void MapTest(void);
private:
    int intTest;
    string stringTest;
    map<string, int> mapTest;
};
TestClass::TestClass(int arg)
{
    cout << "TestClass is constructed here, arg = " << arg << endl;
    intTest = arg;
}
TestClass::~TestClass(void)
{
    cout << "TestClass is destructed" << endl;
}
void TestClass::PrintTest(void)
{
    cout << __FUNCTION__ << " enter" << endl;
    cout << " intTest = " << this->intTest << endl;
}
void TestClass::StringTest(void)
{
    cout << __FUNCTION__ << " enter" << endl;
    string a("Lite");
    string b("OS");
    string c("LiteOS");
    if (a != b) {
        cout << " " << a << " != " << b << endl;
    }
    a += b;
    if (a == c) {
        cout << " " << a << " == " << c << endl;
    }
}
void TestClass::MapTest(void)
{
    cout << __FUNCTION__ << " enter" << endl;
    mapTest.insert(pair<string, int>("Huawei", 1));
    mapTest.insert(pair<string, int>("LiteOS", 2));
    mapTest.insert(pair<string, int>("Open", 3));
    mapTest.insert(pair<string, int>("Source", 4));
    cout << " show map key&value" << endl;
    for (auto &it : mapTest) {
        cout << " " << it.first << " " << it.second << endl;
    }
    mapTest["LiteOS"] = 8; /* 8: new value */
    cout << " change value of \"LiteOS\" key" << endl;
    for (auto &it : mapTest) {
        cout << " " << it.first << " " << it.second << endl;
    }
}
void CppTestEntry(void)
{
    cout << "LiteOS cpp sample start" << endl;
    TestClass test(123);
    test.PrintTest();
    test.StringTest();
    test.MapTest();
    cout << "LiteOS cpp sample stop" << endl;
}
#ifdef __cplusplus
#if __cplusplus
}
#endif /* __cplusplus */
#endif /* __cplusplus */
```
app_init中初始化C++构造函数后，调用C++代码，实现如下：
```
void app_init(void)
{
    ......
    /* 初始化C++构造函数 */
    LOS_CppSystemInit((UINT32)&__init_array_start__, (UINT32)&__init_array_end__, NO_SCATTER);
    /* 调用C++代码 */
    CppTestEntry();
    ......
}
```
#### 结果验证
运行CppTestEntry()函数，结果如下：
```
LiteOS cpp sample start
TestClass is constructed here, arg = 123
PrintTest enter
 intTest = 123
StringTest enter
 Lite != OS
 LiteOS == LiteOS
MapTest enter
 show map key&value
 Huawei 1
 LiteOS 2
 Open 3
 Source 4
 change value of "LiteOS" key
 Huawei 1
 LiteOS 8
 Open 3
 Source 4
LiteOS cpp sample stop
TestClass is destructed
```
#### 完整实例代码
[TestClass.zip](https://support.huaweicloud.com/kernelmanual-LiteOS/resource/TestClass.zip)