What 's the difference between std::string and std:: basic_string ? And why are both needed?

In the C++ standard library, std::string is actually a specialized version of std::basic_string. std::basic_string is a template class designed for creating strings with different character types. Its basic form is std::basic_string, where CharT can be char, wchar_t, char16_t, or char32_t, enabling programmers to handle various character encodings as needed.

std::string

std::string is an alias for std::basic_string, specifically tailored for handling ordinary character sequences. It is the most commonly used string type and is highly effective for processing standard ASCII or UTF-8 text data. As it is based on char, it primarily handles single-byte characters.

std::basic_string

std::basic_string is a more general template class that allows creating strings of different types by specifying the character type. For instance, std::basic_string<wchar_t> is typically used for wide characters (usually UTF-16 or UTF-32), providing better support for internationalization depending on the platform.

Why are both necessary?

1. Flexibility and Generality: std::basic_string provides the capability to create strings for any character type, enabling C++ programs to handle diverse character encodings such as wide characters and multi-byte sequences as required. This is crucial for internationalized software that must support multiple languages.
2. Convenience and Specialization: For most applications, std::string (i.e., std::basic_string) is sufficient. It offers a simple and intuitive interface for text data handling without the complexity of character encoding details, making code easier to write and maintain.

Examples

Suppose you are developing a multi-language text editor; you might use std::basic_string<wchar_t> to process text composed of characters from various languages, as wchar_t better supports different language environments. For example:

cpp
std::basic_string<wchar_t> japanese = L"こんにちは"; // Japanese "Hello"

On the other hand, if you are developing a logging tool that only handles English text, using std::string is adequate:

cpp
std::string message = "Hello, world!";

In summary, std::basic_string enhances the C++ standard library's flexibility and power when handling strings, while std::string provides a specialized version for common needs, simplifying everyday usage.