c++20

Modern C++ Programming Cookbook – Third Edition

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The Third Edition of my book, Modern C++ Programming Cookbook (ISBN 978-1835080542) has been published by Packt. The book can be ordered from Amazon and Packt. The book is organized in recipes, much like a cookbook. These recipes, in turn, are organized in sections that introduce you to the topic, list any necessary pre-requisites and … Read more

Formatting Text in C++: The Old and The New Ways

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When it comes to format a piece of text in C++ there are several ways you can employ: I/O streams, particularly std::stringstream with stream operations (such as operator <<) printf family of functions, particularly sprintf the C++20 format library, particularly std::format / std::format_to any 3rd party library, {fmt} in particular (the source of the new … Read more

requires expressions and requires clauses in C++20

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The C++20 standard added constraints and concepts to the language. This addition introduced two new keywords into the language, concept and requires. The former is used to declare a concept, while the latter is used to introduce a requires expression or a requires clause. These two could be confusion at first, so let’s take a look at which is which and what is their purpose.

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Initializing statement for if/switch/foreach

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There are several statements in C++ whose syntax was modified in recent versions of the standard. I refer here to the if and switch statements that were modified in C++17 to include initializing statements, and the range-based for loop that supports the same as of C++20. Their general form is shown in the following table:

Express one of multiple options in a nice way

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We often find ourselves writing if statements where a variable is compared with several values either to check if it matches one of them or that it doesn’t match any. Here is an example:

int option = ...;

// at lease a value is matched
if (option == 12 || option == 23 || option == 42)
{
   std::cout << "it's a good option\n";
}

// no value is matched
if (option != 12 && option != 23 && option != 42)
{
   std::cout << "it's a bad option\n";
}

This example has three comparison values for each case, but it could be 5, or 10, or any number. If it’s too many then perhaps a different approach should be taken. However, the question is, how do we express this in a simpler way in C++, rather than a long if condition?

The little functions that matter

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Starting with C++20, some very useful functions for searching have been added to some standard containers, such as std::map, std::set, and std::string. These have been required for a long time and it’s good to see that the committee finally agreed upon their value. I hope this is the beginning of some wonderful additions.