C++26 Library: Improved String Processing

In addition to major improvements to reflection and contracts, the upcoming C++26 standard brings several small but useful additions. Today it’s all about strings and stuff string_view,

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First: what is A? string_view,

std::string_view

A std::string_view is a non-owned reference to a string. It represents a view of a string. This string can be a C++ string or a C string. Typically, C++17 provides four types of synonyms for built-in character types.

C++26 Library: Improved String Processing

std::string_view      std::basic_string_view
std::wstring_view     std::basic_string_view
std::u16string_view   std::basic_string_view
std::u32string_view   std::basic_string_view

A question remains: why do we need it? std::string_viewWhy did Google, LLVM and Bloomberg already implement String Views? The answer is simple: it is resource efficient, a std::string_view to copy. One std::string_view Only two pieces of information are needed: the pointer to the string and its length. As you might suspect, they exist std::string_view And its three siblings deal primarily with read operations with the interface std::string consequences. Mainly because they use new methods remove_prefix And remove_suffix Receive.

Test for success or failure ofcharconv> work

Work std::to_chars And std::from_chars It was difficult to test: if(res.ec == std::errc{}),
Here is a simplified program from cpppreference.com,

// charconv.cpp 
 
#include 
#include 
#include 
#include 
#include 
 
template 
void show_to_chars(T value) {
    const size_t buf_size = 5;
    char buf(buf_size);
    std::to_chars_result result = std::to_chars(buf, buf + buf_size, value);
 
    if (result.ec != std::errc{})
        std::cout << std::make_error_code(result.ec).message() << '\n';
    else{
        std::string_view str(buf, result.ptr - buf);
        std::cout << std::quoted(str) << '\n';
    }
}
 
int main() {
    show_to_chars(42);
    show_to_chars(1234567);  
}

Program includes headerscharconv>For character conversion,iomanip>For input/output manipulators,string_view>for the treatment of string_views Andsystem_error>For error handling.

function template show_to_chars takes any kind of value T And tries to convert it to a string. Inside the function, a buffer of size 5 is declared to store the resulting string. Celebration std::to_chars is then called to perform the conversion and bring the result into a std::to_chars_result-object name result To save.

The result object contains a pointer to the end of the converted string and an error code. If the error code is not the same std::errc{} an error message is displayed indicating an error in the conversion. std::make_error_code(result.ec).message() Output to console. otherwise a std::string_viewAn object is created to represent the converted string and is created using a sequence std::quoted Output to the console to make sure it appears within the quotation marks.

In main-function becomes function show_to_chars Called twice: with first value 42 and then with the value 1234567first call converts the value 42 Successfully converts and prints it into a string. However, the second call tries to return the value 1234567 The buffer size to convert exceeds 5, resulting in an error message printed on the console.

Finally the output of the program comes:

Thanks to C++26, the function exists std::to_chars return a boolean and function show_to_chars Can be simplified:

template 
void show_to_chars(T value) {
    std::array str;
    if (auto result = std::to_chars(str.data(), str.data() + str.size(), value)) {
            std::string_view strView(str.data(), result.ptr);
            std::cout << std::quoted(strView) << '\n';
        }
    else
        std::cout << std::make_error_code(result.ec).message() << '\n';
}

inside the function there is a std::array Characters declared with a fixed size of 5 to hold the resulting string. Celebration std::to_chars Then the conversion is called. This function tries to convert a numeric value to a string and put it into an array. str To save. Celebration std::to_chars enters std::to_chars_resultObject that contains a pointer to the end of the converted string and an error code.

function uses one if-Instructions for obtaining results std::to_chars-Call to check. If the conversion is successful, the result object is implicitly converted. true is converted, and the function continues to print the converted string. For this purpose a std::string_view-object strView Generates string from beginning of str– table up to result.ptrThe indicator shows. std::cout-stream is used to output this string view to the console, where std::quoted This ensures that the output is displayed within the quotation marks.

If the conversion fails, the result object is implicitly converted. false is converted and the function returns an error message instead. You get an error message when you make a call std::make_error_code(result.ec).message()Which converts the error code into a human-readable string.
C++26 has additional functions for processing stringSand string_viewS:

• concatenate string stream with std::string_view
• Concatenation of strings and string_views
• arithmetic overload of std::to_string and use of std::format

I have already introduced them in my previous post: “Overview of C++26: Libraries”.

What will happen next?

My next post reveals that there is much more to the C++26 library.

(rme)