QMake - 如何在.pro文件中添加和使用变量

# 定义变量
DEFINES += MY_VARIABLE=1

# 添加头文件路径
INCLUDEPATH += $$PWD/include

# 添加源文件
SOURCES += \
    $$PWD/src/main.cpp \
    $$PWD/src/myclass.cpp

# 添加库文件路径
LIBS += -L$$PWD/lib

# 添加库文件
LIBS += -lmylib

#include<iostream>
#include "myclass.h"

int main() {
#ifdef MY_VARIABLE
    std::cout << "MY_VARIABLE is defined"<< std::endl;
#else
    std::cout << "MY_VARIABLE is not defined"<< std::endl;
#endif

    MyClass myClass;
    myClass.doSomething();

    return 0;
}