{"id":5237,"date":"2017-04-10T19:16:36","date_gmt":"2017-04-10T19:16:36","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/c-17-more-details-about-the-library\/"},"modified":"2017-04-10T19:16:36","modified_gmt":"2017-04-10T19:16:36","slug":"c-17-more-details-about-the-library","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/c-17-more-details-about-the-library\/","title":{"rendered":"C++17- std::byte and std::filesystem"},"content":{"rendered":"

My post, C++17 – What’s New in the Library<\/a>, was fine for the first overview. Today, I will look deeper into the new library. <\/p>\n

<\/p>\n

 <\/p>\n

Let’s start with something new that I didn’t mention in my previous posts:<\/p>\n

\"timeline\"<\/p>\n

std::byte<\/h2>\n

std::byte<\/span> is a distinct type implementing the concept of byte as specified in the C++ language definition. Now we know what a byte is. Therefore, a byte is not an integer or a character and, therefore, not open to programmer errors. Its job is to access object storage. Consequently, its interface consists only of methods for bitwise logical operations.<\/p>\n

 <\/p>\n

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namespace<\/span> std { \r\n\r\n  template<\/span> <class<\/span> IntType<\/span>> \r\n    constexpr byte operator<\/span><<(byte b, IntType shift); \r\n  template<\/span> <class<\/span> IntType<\/span>> \r\n    constexpr byte operator<\/span>>>(byte b, IntType shift); \r\n  constexpr byte operator<\/span>|(byte l, byte r); \r\n  constexpr byte operator<\/span>&(byte l, byte r); \r\n  constexpr byte operator<\/span>~(byte b); \r\n  constexpr byte operator<\/span>^(byte l, byte r); \r\n\r\n} \r\n<\/pre>\n<\/div>\n
 <\/p>\n
You can use the function std::to_integer(std::byte b)<\/span> to convert a std::byte<\/span> to an integer type and the call std::byte{integer}<\/span> to do it the other way around. integer<\/span> has to be a non-negative value smaller than std::numeric_limits<unsigned_char>::max().<\/span><\/p>\n
Now to something you already know.<\/p>\n<\/p>\n
The filesystem library<\/h2>\n
In the post, C++17 – What’s New in the Library<\/a>, I gave a first impression of the filesystem library. The library uses three concepts file, file name, and path. Files can be directories, hard links, symbolic links, or regular files. Paths can be absolute, canonical, or relative. A canonical path includes no symlinks, “.” or “..” elements.<\/p>\n
You can create and remove directories, iterate over them, or check the properties of files.<\/p>\n
 <\/p>\n
\n\n\n\n
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 1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24\r\n25\r\n26\r\n27\r\n28\r\n29\r\n30<\/pre>\n<\/td>\n
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\/\/ filesystem.cpp<\/span>\r\n\r\n#include <fstream><\/span>\r\n#include <iostream><\/span>\r\n#include <string><\/span>\r\n#include <filesystem><\/span>\r\nnamespace<\/span> fs = std::filesystem;\r\n \r\nint<\/span> main(){\r\n\r\n    std::cout << \"Current path: \"<\/span> << fs::current_path() << std::endl;\r\n\r\n    std::string dir= \"sandbox\/a\/b\"<\/span>;\r\n    fs::create_directories(dir);\r\n\r\n    std::ofstream(\"sandbox\/file1.txt\"<\/span>);\r\n    fs::path symPath= fs::current_path() \/=  \"sandbox\"<\/span>;\r\n    symPath \/= \"syma\"<\/span>;\r\n    fs::create_symlink(\"a\"<\/span>, \"symPath\"<\/span>);\r\n    \r\n    std::cout << \"fs::is_directory(dir): \"<\/span> << fs::is_directory(dir) << std::endl;\r\n    std::cout << \"fs::exists(symPath): \"<\/span>  << fs::exists(symPath) << std::endl;\r\n    std::cout << \"fs::symlink(symPath): \"<\/span> << fs::is_symlink(symPath) << std::endl;\r\n    \r\n\r\n    for<\/span>(auto<\/span>& p: fs::recursive_directory_iterator(\"sandbox\"<\/span>))\r\n        std::cout << p << std::endl;\r\n    \/\/ fs::remove_all(\"sandbox\");<\/span>\r\n    \r\n}\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
 <\/p>\n
But there is more to it. So I will now focus on features that are not so obvious. At least for me. I will show you,<\/p>\n