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C++ declspec_01

Date: 2021-01-02Last modified: 2023-09-17

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__declspec is a C++ language extension that allows programmers to specify various attributes or properties of functions and data types in a Microsoft Windows environment. This extension is used to indicate how a particular function or variable should be treated by the compiler or the operating system.

The __declspec extension provides a mechanism to specify various attributes of C++ entities that are specific to the Windows operating system, such as the calling convention, the export or import of functions and data, and the memory allocation model.

Understanding how to use __declspec can be beneficial for developers who need to write code that interacts with the Windows API, creates DLLs or shared libraries, or uses advanced memory management techniques. In this introduction, we will explore the different ways in which __declspec can be used in C++ programming to optimize the performance and functionality of software applications running on the Windows platform.

Não é uma extensão padrão e é válido somente para clang / msvc / intel.

Use as opções -fdeclspec ou -fms-extensions para habilitar

Get and Set

For example, consider a class with private data members that need to be accessed through getter and setter functions. To ensure that these functions are accessed efficiently, you can use __declspec with the appropriate attribute.

class Person {
  int mAge{42};

  int getAge() const {
    cout << "Person::getAge() called here" << endl;
    return mAge;
  void setAge(int value) {
    cout << "Person::setAge(" << value << ") called here" << endl;
    mAge = value;

  __declspec(property(get = getAge, put = setAge)) int age;
  Person person;

  cout << person.age << endl;  // Call person.getAge();
  person.age = 20;             // Call person.setAge(20);

Possible output

Person::getAge() called here
Person::setAge(20) called here