使用 constexpr、SFINAE 和/或 type_traits 重载 char*、char 数组和字符串文字的解析

所以我想我的问题如下:是否有可能在现代 C++ 中区分字符数组和字符串文字? 解决方案 Per [expr.prim.id.unqual]:[...] 表达式的类型是标识符的类型.这结果是由标识符表示的实体.表达式是一个lvalue 如果实体是函数、变量或数据成员，并且否则右值；如果标识符指定一个位域位域([dcl.struct.bind]).因此，给出一个声明const char arr[] = "foo";表达式 arr 是 const char[4] 类型的左值.根据 [lex.string]/8:普通字符串文字和UTF-8字符串文字也被引用作为窄字符串文字.窄字符串文字的类型为数组n const char"，其中 n 是定义的字符串大小下面，并具有静态存储期限.根据 [expr.prim.literal]:A litera 是主要表达方式.它的类型取决于它的形式.一种字符串文字是左值；所有其他文字都是纯右值.因此，表达式 "foo" 是 const char[4] 类型的左值.结论:函数无法区分(const)字符数组和字符串文字.I have run into an interesting challenge that I have been trying to solve for hours, but after much research and many failed attempts, I find myself asking this question.I would like to write 3 overloaded functions that each take one of the following types: const char*, const char(&)[N] and string literal (e.g. "BOO"). I understand that a string literal is simply a char array, but please bear with me while I explain my approach.The two functions below are able to differentiate between the first two types (const char* and const char(&)[N]) thanks to the wrapper class CharPtrWrapper:#include <iostream>class CharPtrWrapper{public: CharPtrWrapper(const char* charPtr) : m_charPtr(charPtr) { } const char * m_charPtr;};void processStr(CharPtrWrapper charPtrWrapper){ std::cout << "From function that takes a CharPtrWrapper = " << charPtrWrapper.m_charPtr << '\n';}template<std::size_t N>void processStr(const char (&charArr)[N]){ std::cout << "From function that takes a \"const char(&)[N]\" = " << charArr << '\n';}int main(){ const char* charPtr = "ABC"; processStr(charPtr); const char charArr[] = {'X', 'Y', 'Z', '\0'}; processStr(charArr);}Output:From function that takes a CharPtrWrapper = ABCFrom function that takes a "const char(&)[N]" = XYZNow, if I call processStr with a string literal (e.g. processStr("BOO")), the version that takes a const char(&)[N] gets called, which makes sense, since a string literal is simply a char array.Here is where I reach the crux of the problem. I have not been able to write a function that is able to differentiate between a char array and a string literal. One thing I thought might work was to write a version that takes an rvalue reference:template<std::size_t N>void processStr(const char (&&charArr)[N]){ std::cout << "From function that takes a \"const char(&&)[N]\" = " << charArr << '\n';}But it turns out that string literals are lvalues. I have also played with different versions that use std::enable_if and std::is_array, but I still don't get the result I'm looking for.So I guess my question is the following: is it possible to differentiate between char arrays and string literals in modern C++? 解决方案 Per [expr.prim.id.unqual]: [...] The type of the expression is the type of the identifier. The result is the entity denoted by the identifier. The expression is an lvalue if the entity is a function, variable, or data member and a prvalue otherwise; it is a bit-field if the identifier designates a bit-field ([dcl.struct.bind]).Therefore, given a declarationconst char arr[] = "foo";The expression arr is an lvalue of type const char[4].Per [lex.string]/8: Ordinary string literals and UTF-8 string literals are also referred to as narrow string literals. A narrow string literal has type "array of n const char", where n is the size of the string as defined below, and has static storage duration.And per [expr.prim.literal]: A litera is a primary expression. Its type depends on its form. A string literal is an lvalue; all other literals are prvalues.Therefore, the expression "foo" is an lvalue of type const char[4].Conclusion: a function is unable to differentiate between a (const) char array and a string literal. 这篇关于使用 constexpr、SFINAE 和/或 type_traits 重载 char*、char 数组和字符串文字的解析的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！