[C++]-VSCode+Makefile编译C++

在《 VSCode+WSL开发环境》中，已经介绍了VSCode+WSL如何进行开发；本文将介绍如何使用makefile来编译C++程序。

开发

以编译子文件夹下的文件为例，目录结构如下：

C++源文件

源文件中，以vector为例，如何使用移动构造，以及快速清空vector：

#include 
#include 
#include 
#include 
#include 

class DemoPrint
{
    int data{0};

public:
    DemoPrint(int init) : data(init)
    {
        std::cout << "DemoPrint constructor " << data << std::endl;
    }

    DemoPrint(DemoPrint &&demo) : data(demo.data + 10)
    {
        std::cout << "DemoPrint move-structor " << data << std::endl;
    }

    ~DemoPrint()
    {
        std::cout << "DemoPrint destructor " << data << std::endl;
    }
};

void vectorClearTest()
{
    std::vector vec;
    vec.push_back(DemoPrint(1));
    std::cout << "after push back, size:" << vec.size() << ", capacity:" << vec.capacity() << std::endl;
    vec = decltype(vec){};
    std::cout << "after assigned, size:" << vec.size() << ", capacity:" << vec.capacity() << std::endl;

    vec.push_back(DemoPrint(2));
    std::cout << "after re-push back, size:" << vec.size() << ", capacity:" << vec.capacity() << std::endl;
    (decltype(vec){}).swap(vec);
    std::cout << "after swapped, size:" << vec.size() << ", capacity:" << vec.capacity() << std::endl;

    vec.push_back(DemoPrint(3));
    vec.clear();
}

void weakPtrTest()
{
    std::weak_ptr wp{};
    if (wp.expired())
    {
        std::cout << "Empty WP expired" << std::endl;
    }

    {
        std::shared_ptr sp(new int(1));
        wp = sp;
        if (wp.expired())
        {
            std::cout << "Inscope WP expired" << std::endl;
        }
        if (sp)
        {
        }
    }

    if (wp.expired())
    {
        std::cout << "Outscope WP expired" << std::endl;
    }
}

int main()
{
    vectorClearTest();
    
    std::optional oi;
    if (!oi)
    {
        std::cout << "optional is empty" << std::endl;
    }

    oi = 12;
    if (oi)
    {
        std::cout << "optional value: " << oi.value() << std::endl;
    }

    sleep(10);
    std::cout << "main quit." << std::endl;
    return 0;
}

Makefile

VSCode启动运行时，只会调用最顶层的Makefile，为能编译子文件下的文件，需要在顶层Makefile中调用子文件夹下的Makefile。

顶层Makefile（调用子文件夹下Makefile）：

subsystem:
	cd learning && make

clean:
	cd learning && make clean

运行make会自动编译，而运行make clean会做清理；

子文件夹Makefile（真正编译文件）：

CFLAGS=-c -Wall -std=c++17
LFLAGS = -Wall -std=c++17
CXXFLAGS = -Wall -std=c++17


hello: hello.o
	g++ -g -std=c++17 -o hello hello.o

hello.o: hello.cpp
	g++ -g -std=c++17 -o hello.o -c hello.cpp
	
clean:
	rm -rf hello
	rm -rf *.o

为保证能支持C++17，必须设定标志CXXFLAGS，否则即使g++中添加了-std=c++17也无效。

VSCode配置

为例使用make编译，需要修改.vscode目录下的tasks.json文件

task

默认生成的task使用g++编译，需要修改为使用make：

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build", 
            "command": "make", 
            "type": "shell",
            "group": {
                "kind": "build",
                "isDefault": true
            }
        },
        {
            "label": "clean",
            "command": "make", // 在shell中使用命令，如需加参数，可再添加args属性
            "args": [
                "clean"
            ],
            "type": "shell",
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ]
}

同时要保证launch.json中preLaunchTask的值与此文件中label的值相同。

properties

为使vscode识别C++17，需要修改c_cpp_properties.json中cppStandard：

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/**"
            ],
            "defines": [],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "c11",
            "cppStandard": "c++17",
            "intelliSenseMode": "linux-gcc-x64"
        }
    ],
    "version": 4
}