C++ Standard Library |

\n`` is C++ A header file in the standard library that provides functions for handling wide characters (`wchar_t`）and wide string functions. Most of these functions come from C standard library's ``，Used for processing wide character input/output, memory operations, string operations and other wide character related functions.\n\n## Syntax\n\n`cwchar` Functions defined in header file usually have names similar to standard character processing functions, but starting with `w` beginning, for example `wprintf`、`wscanf` etc. The parameters and return types of these functions also differ from corresponding standard character functions, they use wide character type `wchar_t`。\n\n### Basic Types\n\n*   `wchar_t`：Wide character type, used to store wide characters.\n*   `wint_t`：Used to store return value of wide character functions.\n\n## Common functions\n\n### 1. **Wide character input/output**\n\n*   `fgetwc`：Read wide characters from file stream.\n*   `fputwc`：Write wide character to file stream.\n*   `fgetws`：Read wide string from file stream.\n*   `fputws`：Write wide string to file stream.\n\n## Example\n\n```cpp\n#include \n#include \n\nint main(){\n    // Use fputws and fgetws for wide string input/output\n    const wchar_t* filename = L"example.txt";\n    FILE* file = std::fopen("example.txt", "w");\n    if(file){\n        std::fputws(L"Hello, World!n", file);\n        std::fclose(file);\n    }\n    file = std::fopen("example.txt", "r");\n    if(file){\n        wchar_t buffer;\n        if(std::fgetws(buffer, 256, file)){\n            std::wcout << L"Read from file: " << buffer;\n        }\n        std::fclose(file);\n    }\n    return 0;\n}\n\nThe output result is:\n\nRead from file: Hello, World!\n\n### 2. **Wide character and wide string operations**\n\n*   `wcscpy`：Copy wide string.\n*   `wcslen`：Get Wide string length。\n*   `wcscmp`：Compare wide strings.\n*   `wcsncpy`：Copy wide string of specified length.\n\n## Example\n\n```cpp\n#include \n#include \n\nint main(){\n    wchar_t str1 = L"Hello";\n    wchar_t str2 = L"World";\n    // Wide string copy\n    std::wcscpy(str1, L"Hello, World!");\n    std::wcout << L"Copied string: " << str1 << std::endl;\n    // Wide string length\n    size_t len = std::wcslen(str1);\n    std::wcout << L"Length of string: " << len << std::endl;\n    // Wide string comparison\n    int result = std::wcscmp(str1, str2);\n    std::wcout << L"Comparison result: " << result << std::endl;\n    // Partial copy of wide string\n    std::wcsncpy(str2, str1, 5);\n    str2 = L''; // Ensure null-terminated\n    std::wcout << L"Partially copied string: " << str2 << std::endl;\n    return 0;\n}\n\nThe output result is:\n\nCopied string: Hello,\n\n### 3. **Wide character classification and conversion**\n\n*   `iswalpha`：Check if wide character is a letter.\n*   `iswdigit`：Check if wide character is a digit。\n*   `towlower`：Convert wide character to lowercase.\n*   `towupper`：Convert wide character to uppercase.\n\n## Example\n\n```cpp\n#include \n#include \n\nint main(){\n    wchar_t ch = L'A';\n    // Check if wide character is a letter\n    if(std::iswalpha(ch)){\n        std::wcout << ch << L" is an alphabetic character." << std::endl;\n    }\n    // Check if wide character is a digit\n    ch = L'9';\n    if(std::iswdigit(ch)){\n        std::wcout << ch << L" is a digit." << std::endl;\n    }\n    // Convert wide character to lowercase\n    ch = L'G';\n    wchar_t lower_ch = std::towlower(ch);\n    std::wcout << L"Lowercase of " << ch << L" is " << lower_ch << std::endl;\n    // Convert wide character to uppercase\n    ch = L'a';\n    wchar_t upper_ch = std::towupper(ch);\n    std::wcout << L"Uppercase of " << ch << L" is " << upper_ch << std::endl;\n    return 0;\n}\n\nThe output result is:\n\nA is an alphabetic character.9 is a digit.Lowercase of G is g Uppercase of a is A\n\n### 4. **Input/output of wide characters and wide strings**\n\n*   `wprintf`：Formatted output of wide characters.\n*   `wscanf`：Formatted input of wide characters.\n*   `swprintf`：Write formatted wide characters to wide string。\n*   `swscanf`：Read formatted wide characters from wide string。\n\n## Example\n\n```cpp\n#include \n#include \n\nint main(){\n    wchar_t buffer;\n    // Formatted output of wide characters\n    std::wprintf(L"Formatted output: %d %sn", 42, L"Hello");\n    // Formatted input of wide characters\n    std::wprintf(L"Enter a number and a string: ");\n    std::wscanf(L"%d %ls", &buffer);\n    std::wprintf(L"You entered: %lsn", buffer);\n    // Write formatted wide characters to wide string\n    std::swprintf(buffer, 100, L"Formatted %d %s", 42, L"output");\n    std::wcout << L"Buffer: " << buffer << std::endl;\n    // Read formatted wide characters from wide string\n    int number;\n    wchar_t word;\n    std::swscanf(buffer, L"Formatted %d %s", &number, word);\n    std::wcout << L"Parsed number: " << number << L", word: " << word << std::endl;\n    return 0;\n}\n\nThe output result is:\n\nFormatted output: 42 H Enter a number and a string:  You entered: Buffer: Formatted 42 o Parsed number: 42, word: o\n\n