std ctype byname in C++
The std::ctype_byname is a function (a specialization of a generic interface) within the C++ <locale> header that allows you to create character classification objects based on specific named locales. In simpler terms, it helps you to determine how characters are categorized (uppercase, lowercase, digit, etc.) according to different language conventions.
Declaration:
template< class CharT >
class ctype_byname : public std::ctype<CharT>;
Character categorization criteria specific to the locale chosen during creation are included in the std::ctype_byname and std::ctype function.
Key Points of the std::ctype_byname:
- Template-Based: It is declared as template<typename _CharT> class std::ctype_byname.
- Locale-Specific: It takes a locale name (e.g., "en_US", "fr_FR") during construction to define character classification rules.
- Overrides Base Class: It inherits from std::ctype<_CharT> and overrides its member functions to provide locale-specific behavior.
Locales:
A locale in C++ represents a particular language and cultural setting. It influences how things like formatting (dates, numbers, currency), collation (sorting order), and character classification are handled.
Example:
Let us take an example to illustrate how to create a std::ctype_byname Object in C++:
#include <iostream>
#include <locale>
#include <string>
int main() {
// Create a ctype object for the US English locale
std::locale loc("en_US.UTF-8");
const std::ctype<char>& us_ctype = std::use_facet<std::ctype<char>>(loc);
// Create a ctype_byname object for French Canadian locale
std::string french_canada_locale = "fr_CA.UTF-8";
const std::ctype<char>& ca_fr_ctype = std::use_facet<std::ctype<char>>(std::locale(french_canada_locale));
// ... (use us_ctype and ca_fr_ctype for character classification)
return 0;
}
Output:
![std::ctype_byname in C++](https://static.tutorialandexample.com/cpp/std-ctype-byname-in-cpp1.png)
Using std::ctype_byname for Character Classification:
Just like the standard std::ctype function, std::ctype_byname provides various member functions to categorize characters:
- isupper(c): It checks if character c is uppercase.
- islower(c): It checks if character c is lowercase.
- isdigit(c): It checks if character c is a digit.
- isalnum(c): It checks if character c is alphanumeric.
The behavior of these functions will differ based on the chosen locale. For example, isupper('E') might return true for the US English locale but false for a locale where uppercase 'E' doesn't exist.
Example:
Let us take an example to illustrate the std::ctype_byname() function in C++.
#include <iostream>
#include <locale>
#include <sstream>
struct csv_ws : std::ctype<wchar_t> {
bool do_is(mask m, char_type c) const {
if ((m & space) && c == L' ')
return false;
if ((m & space) && c == L',')
return true;
return ctype::do_is(m, c);
}
};
int main() {
std::wstring inp;
inp += L"Col1,Col2,Col3\n";
inp += L"123,456,789";
std::wstring tok;
std::wcout << "Default locale:\n";
std::wistringstream stream1(inp);
while (stream1 >> tok)
std::wcout << " " << tok << '\n';
std::wcout << "Modified locale:\n";
std::wistringstream stream2(inp);
csv_ws* my_ws = new csv_ws;
stream2.imbue(std::locale(stream2.getloc(), my_ws));
while (stream2 >> tok)
std::wcout << " " << tok << '\n';
delete my_ws;
}
Output:
![std::ctype_byname in C++](https://static.tutorialandexample.com/cpp/std-ctype-byname-in-cpp2.png)
Benefits of std::ctype_byname:
Several benefits of the std::ctype_byname() function are as follows:
- Locale-Aware Character Classification: Character classification that takes locale into account. This guarantees precise character classification according to the target language.
- Flexibility: It allows you to switch locales dynamically within your program.
- Example: Case-Insensitive Comparison with Different Locales
Advanced Techniques with std::ctype_byname
Beyond basic character classification, std::ctype_byname function opens doors to more sophisticated locale-aware operations:
Internationalization (i18n): By leveraging std::ctype_byname and other locale facilities, you can create applications that can be easily adapted to different languages and regions, enhancing their global reach.ce more dependable and durable code.
Custom Facet Creation: You can subclass std::ctype_byname to define your own character classification rules based on specific needs.
Custom Locale Creation: The <locale> header file offers tools to construct custom locales that combine elements from different named locales, allowing for even finer-grained control over character behavior.