如何在 C 編譯時檢索模板參數類型名稱？

Type Name Retrieval in C++ Templates

In C++, templates provide a powerful mechanism for creating generic classes and functions. However, obtaining the name of the template parameter type can be challenging, especially when handling exceptions that indicate data parse errors. This article explores a compile-time solution to retrieve the type name in templates, avoiding runtime performance overhead.

The original challenge involved writing template classes for parsing data files. The aim was to provide meaningful error messages in the event of parse errors, including the type name the template function attempted to parse.

The sample code provided attempted to use boost::lexical_cast to convert the value to the desired type, throwing an exception if the conversion failed. However, it lacked a mechanism to retrieve the type name for use in the exception message.

The accepted solution leverages the typeid(T) function, which returns a std::type_info object. The name() method of std::type_info returns a null-terminated character array containing the type name, providing the desired functionality. The code snippet below illustrates the modification:

try {
    return boost::lexical_cast<T>(it->second);
} catch (...) {
    throw ParseError(file, section, key, it->second, typeid(T).name());
}

By utilizing typeid(T).name(), the type name is obtained at compile time, eliminating any runtime performance overhead. This approach ensures that error messages include detailed information about the expected type, enhancing user experience and facilitating error debugging.

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