std::codecv..._max_length(3)

🎀 std::codecvt::max_length + do_max_length 🎀

Okay so hi bestie!! 💖 This page lives in the C++ Standard Libary manual — yes, that spelling is exactly what the header says, we're keeping it — and the page name is std::codecv..._max_length(3). It's giving “tiny max-length function, main character energy,” so let's go. 🦋

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🌸 NAME 🌸

std::codecvt::max_length,do_max_length — std::codecvt::max_length,do_max_length. Yep, the NAME line repeats itself and we are not erasing the duplicate, bestie. 💅

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🛠️ Synopsis 🛠️

Defined in header <locale>:

public:                                             (until C++11)
int max_length() const throw();
public:                                             (since C++11)
int max_length() const noexcept;            (1)
protected:
(until C++11)
virtual int do_max_length() const throw();      (2)
protected:
(since C++11)
virtual int do_max_length() const noexcept;

1. Public member function — it calls the member function do_max_length of the most derived class.
2. Returns the maximum value that do_length(state, from, from_end, 1) can return for any valid range [from, from_end) and any valid state.

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💖 Return value 💖

The maximum number of ExternT characters that could be consumed if converted by in() to produce one InternT character. 🫶

The non-converting specialization std::codecvt<char, char, std::mbstate_t> returns 1. Slay. ✨

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🧠 Notes 🧠

If the encoding is state-dependent (encoding() == -1), then more than max_length() external characters may be consumed to produce one internal character. Heads up, bestie: that's the state-dependent plot twist. 🫠

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🎬 Example 🎬

The example literally starts with // Run this code, so go off: 💻

#include <codecvt>
#include <iostream>
#include <locale>

int main()
{
    std::cout << "In codecvt_utf8, the longest multibyte character is "
              << std::codecvt_utf8<wchar_t>().max_length() << " bytes long\n";

    std::cout << "In header-consuming codecvt_utf8, the longest multibyte character is "
              << std::codecvt_utf8<wchar_t,
                                   0x10ffff,
                                   std::consume_header>().max_length()
              << " bytes long\n";

    std::cout << "In this system's en_US.utf8, the longest multibyte character is "
              << std::use_facet<std::codecvt<wchar_t, char,
                                             std::mbstate_t>>(
                     std::locale("en_US.utf8")
                 ).max_length() << " bytes long\n";

    std::cout << "In this system's zh_CN.gb18030, the longest multibyte character is "
              << std::use_facet<std::codecvt<wchar_t, char,
                                             std::mbstate_t>>(
                     std::locale("zh_CN.gb18030")
                 ).max_length() << " bytes long\n";
}

💻 Output: 💻

In codecvt_utf8, the longest multibyte character is 4 bytes long
In header-consuming codecvt_utf8, the longest multibyte character is 7 bytes long
In this system's en_US.utf8, the longest multibyte character is 6 bytes long
In this system's zh_CN.gb18030, the longest multibyte character is 4 bytes long

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👀 See also 👀

• MB_CUR_MAX — maximum number of bytes in a multibyte character in the current C locale (macro variable). 🌈
• do_encoding — [virtual] returns the number of ExternT characters necessary to produce one InternT character, if constant (virtual protected member function). 🧚

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Byeeee bestie!! 💋 This page's source/version is http://cppreference.com, its date is 2024.06.10, and it's the std::codecv..._max_length(3) page. Periodt. 👑