C ++中类定义前面的宏是什么意思

本文介绍了C ++中类定义前面的宏是什么意思的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

C ++中允许以下构造的语法是什么，在 class和 class_name之间出现一个单词？

What is the syntax in C++ that allows the following construction, where a word appears in between "class" and "class_name"?

namespace octave { // Command line arguments. See also options-usage.h. class OCTINTERP_API cmdline_options { public: ...

注意，我并不是在问宏的含义。我不是在问它做什么。我不是问它是否为空。我在问类定义的语法。

Note, I am not asking the meaning of the macro. I am not asking what it does. I am not asking if it is empty. I am asking about the syntax of class definition.

一些资料解释了语法，但是中间没有单词，例如：

Several sources explain the syntax, but without the word in the middle, for example:

class class_name { access_specifier_1: member1; access_specifier_2: member2; ... } object_names;

还请注意以下有关语法的问题和答案与其他有关： 在c ++中的类定义前面的宏和 C ++类定义语法

Note also that the following questions asked about the syntax and the answers were about something else: macro in front of class definition in c++ and C++ Class definition syntax

推荐答案

它不是标准的C ++（除非宏评估为空格，或者您使用的是属性），但是某些编译器在针对特定平台时需要使用它。

It's not standard C++ (unless the macro evaluates to whitespace, or you're using attributes) but it's required by some compilers when targeting certain platforms.

常见的情况是在为Windows构建动态链接库（dll）时。生成dll时， OCTINTERP_API 可能设置为 __ declspec（dllexport），而 __ declspec（dllimport ）（使用dll时）。

A common occurrence is when building a dynamic linked library (dll) for Windows. OCTINTERP_API is likely set to __declspec(dllexport) when building the dll, and __declspec(dllimport) when using the dll.

（请参见 en.cppreference/w/cpp/language/classes ）