Stdctypewiden And Do Widen In C++

Character management is essential in text processing in C++. On the other hand, representations of characters can change greatly between locales and encoding methods. In order to make handling characters easier, C++ has the std::ctype class template, which comes with operations like std::ctype::dowiden and std::ctype::widen. In this article, we will discuss the std::ctype::widen and std::ctype::dowiden with its syntax and example.

What is the std::ctype?

Fundamentally, std::ctype function works as a locale-specific aspect that handles character conversion and classification. It allows developers to interact with characters in a locale-aware way by encapsulating locale-specific rules guiding character behavior. Among all of its many features, character conversion is one of the most important feature because it allows characters to be represented both inside and externally.

What is the std::ctype::widen?

The std::ctype class template includes the std::ctype::widen function. Characters are converted between the external and internal representations that the C++ locale uses. It returns the equivalent character in the internal representation after receiving a single argument of type char, which represents the character that has to be converted.

Syntax:

It has the following syntax:

wchar_t widen(char c) const;

Example:

Let us take an example to illustrate the std::ctype::widen in C++.

#include<iostream>
#include<locale>
int main() {
    // Create a locale object representing the default locale
    std::locale loc;
    // Obtain a reference to the std::ctype<char> facet of the current locale
    const std::ctype<char>& ct = std::use_facet<std::ctype<char>>(loc);
    // Define an external character
    char externalChar = 'A';
    // Convert the external character to its internal representation
    wchar_t internalChar = ct.widen(externalChar);
    // Print both the external and internal characters
    std::cout << "External char: " << externalChar << std::endl;
    std::wcout << "Internal char: " << internalChar << std::endl;
    return 0;
}

Output:

Code Explanation:

Create Locale Object:

• ✅ In this example, a locale object loc is created to reflect the system's default locale.

Obtain ctype function:

• ✅ A reference to the std::ctype function of the current locale is obtained by using std::use_facet<std::ctype>(loc).
• ✅ This aspect offers tools for categorizing and converting characters according to the regulations of the current region.

Define External Character:

• ✅ A character in the external encoding scheme is represented by the external character externalChar, which is defined with the value 'A'.

Character Conversion:

• ✅ The std::ctype::widen function is called on the ctype facet (ct) to convert the external character externalChar to its internal representation.
• ✅ This function can translate a single-byte external character into its matching wide-character internal representation.

What is the std::ctype::do_widen?

The std::ctype::do_widen function is a virtual member function in the std::ctype class template. This function carries out the actual character conversion between the exterior and internal representations. Derived classes override this function to offer locale-specific character conversion behavior.

Syntax:

It has the following syntax:

virtual wchar_t do_widen(char c) const;

Example:

Let us take an example to illustrate the std::ctype::do_widen in C++.

#inlcude<iostream>
#include<locale>
class MyCustomCType : public std::ctype<wchar_t> {
public:
    explicit MyCustomCType(size_t refs = 0) : std::ctype<wchar_t>(refs) {}
protected:
    wchar_t do_widen(char c) const override {
        return L'x'; // Custom conversion logic: convert any character to 'x'
    }
};
int main() {
    std::locale loc(std::locale(), new MyCustomCType);
    const MyCustomCType& ct = std::use_facet<MyCustomCType>(loc);
    char externalChar = 'A';
    wchar_t internalChar = ct.widen(externalChar);
    std::wcout << "External char: " << externalChar << std::endl;
    std::wcout << "Internal char: " << internalChar << std::endl;
    return 0;
}

Output:

Code Explanation:

Override Character Conversion:

• ✅ In this example, the MyCustomCType class overrides the do_widen function.
• ✅ Converting an external character (char) to its internal representation (wchar_t) is the responsibility of this virtual function.
• ✅ Any external character in this custom implementation is changed to the internal character "x".

Locale Formation:

• ✅ A locale object loc is produced using the constructor std::locale and the default parameters.

Integrating Custom Facets:

• ✅ The custom ctype facet MyCustomCType is incorporated into the locale loc bypassing it as a parameter to the constructor std::locale(loc, new MyCustomCType).

Obtaining Facets:

• ✅ A reference to the locale loc's MyCustomCType facet is retrieved and saved in ct using std::use_facet(loc).

External Character Encoding:

• ✅ ExternalChar is defined as an external character with the value 'A'.

Character Conversion:

• ✅ The external character externalChar is converted to its internal representation, which is stored in internalChar, by calling the broaden function of the custom ctype facet ct.

Another Example:

Let us take another C++ program to demonstrate std::ctype::widen and std::ctype::do_widen.

#include<iostream>
#inlcude<locale>
class MyCustomCType : public std::ctype<wchar_t> {
public:
    explicit MyCustomCType(size_t refs = 0) : std::ctype<wchar_t>(refs) {}
public:
    wchar_t do_widen(char c) const override {
        // Custom conversion logic for do_widen: convert any character to 'x'
        return L'x';
    }
};
int main() {
    // Create a locale object with a custom ctype facet
    std::locale loc(std::locale(), new MyCustomCType);
    // Get a reference to the custom ctype facet
    const MyCustomCType& ct = std::use_facet<MyCustomCType>(loc);
    // Define an external character
    char externalChar = 'A';
    // Convert the external character to internal representation using std::ctype::widen
    wchar_t internalCharWiden = ct.widen(externalChar);
    // Convert the external character to internal representation using the custom do_widen function
    wchar_t internalCharDoWiden = ct.do_widen(externalChar);
    // Print both internal characters
    std::wcout << "Using std::ctype::widen:" << std::endl;
    std::wcout << "External char: " << externalChar << std::endl;
    std::wcout << "Internal char: " << internalCharWiden << std::endl;
    std::wcout << "\nUsing custom do_widen function:" << std::endl;
    std::wcout << "External char: " << externalChar << std::endl;
    std::wcout << "Internal char: " << internalCharDoWiden << std::endl;
    return 0;
}

Output: