{"id":8071,"date":"2023-08-21T07:37:20","date_gmt":"2023-08-21T07:37:20","guid":{"rendered":"https:\/\/www.modernescpp.com\/?p=8071"},"modified":"2024-05-05T09:17:11","modified_gmt":"2024-05-05T09:17:11","slug":"c23-a-modularized-standard-library-stdprint-and-stdprintln","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/c23-a-modularized-standard-library-stdprint-and-stdprintln\/","title":{"rendered":"C++23: A Modularized Standard Library, std::print and std::println"},"content":{"rendered":"\n

The C++23 standard library has very impressive improvements. In this post, I will write about the modularized standard library and the two convenience functions std::print<\/code> and std::println<\/code>.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

<\/span>The new “Hello World”<\/span><\/h2>\n\n\n\n

Each programming challenge in a new language starts with the “Hello World” program. Since C++98, this was our starting point: <\/p>\n\n\n\n

#include <iostream><\/span>\n\nint<\/span> main<\/span>() {\n\n    std::<\/span>cout <<<\/span> "Hello World<\/span>\\n<\/span>"<\/span>; \n\n}\n<\/pre><\/div>\n\n\n\n
Honestly, you have to skip your old habits in C++23. Here is the current “Hello World program:<\/p>\n\n\n\n
import std;\n\nint<\/span> main<\/span>() {\n\n    std::<\/span>println("Hello World"<\/span>); \n\n}\n<\/pre><\/div>\n\n\n\n
Let me analyze the program.<\/p>\n\n\n\n
<\/span>Modularized Standard Library<\/span><\/h2>\n\n\n\n
C++23 supports a modularized standard library. You say import std;<\/code>, and you get the entire standard library. If you also want the global C functions such as printf<\/code>, you must use import std.compat;<\/code>. Here is the corresponding “Hello World” program using printf<\/code>.<\/p>\n\n\n\n
import std.compat;\n\nint<\/span> main<\/span>() {\n\n    printf("Hello World<\/span>\\n<\/span>"<\/span>); \n\n}\n<\/pre><\/div>\n\n\n\n
<\/p>\n\n\n\n
The modularized standard library has two significant improvements: a significantly improved compilation time and usability.<\/p>\n\n\n\n
<\/span>Significantly improved Compilation Time<\/span><\/h3>\n\n\n\n
Importing the standard library (import std) is literally for free. This means that the compilation times will drop significantly. The first experience numbers state that the complication times became faster by at least a factor of 10. The reason for this improvement is evident. Instead of successively expanding your header files, you import a module. For that reason, there is only one module you have to import only once. So far, only the MSVC compiler supports this C++23 feature: Tutorial: Import the C++ standard library using modules from the command line<\/a>.<\/p>\n\n\n\n
<\/span>Usability<\/span><\/h3>\n\n\n\n
Assume you want to use the function std::accumulate<\/code>. Do you know which header you have to include? Is it <numeric><\/code>, <functional><\/code>, or <algorithm><\/code>. Maybe, this was too easy for you. So what about std::forward<\/code>, or why does the following program fail to compile? <\/p>\n\n\n\n
int<\/span> main<\/span>() {\n\n    auto<\/span> list =<\/span> {1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>};\n\n}\n<\/pre><\/div>\n\n\n\n
The {1, 2, 3, 4} is a std::initializer_list<int>. <\/code><\/p>\n\n\n\n
To use it, you have to include the header <initializer_list><\/code>. Of course, this header is automatically included when you use a container like std::vector<\/code>.  <\/code><\/p>\n\n\n\n
Compare this with an import std;<\/code> or import std::compat; <\/code>and you are done. I know from my experience. Not only beginners often fail to use the correct header.<\/p>\n\n\n\n
I didn’t know if you recognized it, but my C++23-ish “Hello World” program used a second feature of C++23:<\/p>\n\n\n\n
<\/span>std::print<\/code> and std::println<\/code><\/span><\/h2>\n\n\n\n
The C++23 supports for both functions two overloads:<\/p>\n\n\n\n