{"id":5027,"date":"2016-11-13T19:35:27","date_gmt":"2016-11-13T19:35:27","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/constexpr-variables-and-objects\/"},"modified":"2023-06-26T12:36:21","modified_gmt":"2023-06-26T12:36:21","slug":"constexpr-variables-and-objects","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/constexpr-variables-and-objects\/","title":{"rendered":"constexpr – Variables and Objects"},"content":{"rendered":"

If you declare a variable as constexpr<\/span> the compiler will evaluate them at compile time. This holds not only true for built-in types but also for instantiations of user-defined types. There are a few serious restrictions for objects to evaluate at compile time.<\/p>\n

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To make it easier, I will use built-in types like bool, char, int<\/span>, and double<\/span>. I will call the remaining data types user-defined data types. These are, for example, std::string,<\/span> types from the C++ library, and user-defined data types. User-defined types typically hold built-in types.<\/p>\n

Variables<\/h2>\n

By using the keyword constexpr<\/span> the variable becomes a constant expression.<\/p>\n

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constexpr double<\/span> myDouble= 5.2;\r\n<\/pre>\n<\/div>\n
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Therefore, I can use the variable in contexts requiring constant expression. For example, if I want to define the size of an array. This has to be done at compile time.<\/p>\n
For the declaration of constexpr<\/span> variable, you have to keep a few rules in mind.<\/p>\n
The variable<\/p>\n