在失败的 If 语句中调用 Switch 语句

Question

抱歉，如果标题具有误导性或笼统。我真的不知道还有什么可以命名的标题。我创建了一个函数，可以将任何类型的向量转换为字符串。我有 template<typename K> 前面的函数代码，它用作向量类型的占位符。我的主要问题是用于检查向量类型的 if 语句中的嵌套 switch 语句。即使 if 语句检查失败，代码仍然会出现此错误：a switch expression of type 'float' is not valid。例如，如果我在 main 中声明了一个 float 类型的向量，那么我使用该函数将向量转换为字符串，它会给我两个错误。一个用于嵌套在int 检查内的switch 语句，另一个用于嵌套在char 检查内的switch 语句。这是非常令人沮丧的，因为如果由于向量不是int 或char 而导致检查失败。此外，它们也不能同时是int 和char！我一直在尝试剖析我的代码并解决这个问题，但我没有找到解决方案。也许是因为我不熟悉模板和 std::is_same 函数。

这是我的头文件代码（有点长）：

#include <string>
#include <vector>

//Converts a vector of any type into a string like this: 2, 5, 6, 3, (Yes the comma stays at the end like that. That can be fixed but it will require huge amounts of code)
template<typename K>
std::string convertToString(std::vector<K>& V) {

    std::string result_str{""};

    for (auto s : V) {

        if (std::is_same<K, bool>::value) {

            if (s == true) {

                result_str += "true, ";

            }
            else if (s == false) {

                result_str += "false, ";

            }

        }
        else if (std::is_same<K, int>::value) {

            switch (s) {

            case 1:
                result_str += "1, ";
                break;

            case 2:
                result_str += "2, ";
                break;

            case 3:
                result_str += "3, ";
                break;

            case 4:
                result_str += "4, ";
                break;

            case 5:
                result_str += "5, ";
                break;

            case 6:
                result_str += "6, ";
                break;

            case 7:
                result_str += "7, ";
                break;

            case 8:
                result_str += "8, ";
                break;

            case 9:
                result_str += "9, ";
                break;

            default:
                result_str += "Not a digit, ";

            }

        }
        else if (std::is_same<K, float>::value) {

            //Because switch statements cannot take floating point values (For some reason I thought this would fix my problem but it didn't)
            if (s == 1) {

                result_str += "1, ";

            }
            else if (s == 2) {

                result_str += "2, ";

            }
            else if (s == 3) {

                result_str += "3, ";

            }
            else if (s == 4) {

                result_str += "4, ";

            }
            else if (s == 5) {

                result_str += "5, ";

            }
            else if (s == 6) {

                result_str += "6, ";

            }
            else if (s == 7) {

                result_str += "7, ";

            }
            else if (s == 8) {

                result_str += "8, ";

            }
            else if (s == 9) {

                result_str += "9, ";

            }
            else {
                result_str += "., ";
            }

        }
        else if (std::is_same<K, char>::value) {

            switch (s)
            {
            case 'a': 
                result_str += "a, ";
                break;

            case 'A':
                result_str += "A, ";
                break;

            case 'b': 
                result_str += "b, ";
                break;

            case 'B':
                result_str += "B, ";
                break;

            case 'c': 
                result_str += "c, ";
                break;

            case 'C':
                result_str += "C, ";
                break;

            case 'd': 
                result_str += "d, ";
                break;

            case 'D':
                result_str += "D, ";
                break;

            case 'e': 
                result_str += "e, ";
                break;

            case 'E':
                result_str += "E, ";
                break;

            case 'f': 
                result_str += "f, ";
                break;

            case 'F':
                result_str += "F, ";
                break;

            case 'g': 
                result_str += "g, ";
                break;

            case 'G':
                result_str += "G, ";
                break;

            case 'h':
                result_str += "h, ";
                break;

            case 'H':
                result_str += "H, ";
                break;

            case 'i':
                result_str += "i, ";
                break;

            case 'I':
                result_str += "I, ";
                break;

            case 'j': 
                result_str += "j, ";
                break;

            case 'J':
                result_str += "J, ";
                break;

            case 'k': 
                result_str += "k, ";
                break;

            case 'K':
                result_str += "K, ";
                break;

            case 'l': 
                result_str += "l, ";
                break;

            case 'L':
                result_str += "L, ";
                break;

            case 'm': 
                result_str += "m, ";
                break;

            case 'M':
                result_str += "M, ";
                break;

            case 'n': 
                result_str += "n, ";
                break;

            case 'N':
                result_str += "N, ";
                break;

            case 'o': 
                result_str += "o, ";
                break;

            case 'O':
                result_str += "O, ";
                break;

            case 'p': 
                result_str += "p, ";
                break;

            case 'P':
                result_str += "P, ";
                break;

            case 'q': 
                result_str += "q, ";
                break;

            case 'Q':
                result_str += "Q, ";
                break;

            case 'r': 
                result_str += "r, ";
                break;

            case 'R':
                result_str += "R, ";
                break;

            case 's': 
                result_str += "s, ";
                break;

            case 'S':
                result_str += "S, ";
                break;

            case 't': 
                result_str += "t, ";
                break;

            case 'T':
                result_str += "T, ";
                break;

            case 'u': 
                result_str += "u, ";
                break;

            case 'U':
                result_str += "U, ";
                break;

            case 'v': 
                result_str += "v, ";
                break;

            case 'V':
                result_str += "V, ";
                break;

            case 'w': 
                result_str += "w, ";
                break;

            case 'W':
                result_str += "W, ";
                break;

            case 'x':
                result_str += "x, ";
                break;

            case 'X':
                result_str += "X, ";
                break;

            case 'y': 
                result_str += "y, ";
                break;

            case 'Y':
                result_str += "Y, ";
                break;

            case 'z': 
                result_str += "z, ";
                break;

            case 'Z':
                result_str += "Z, ";
                break;
            }

        }

    }

    return result_str;

}

这是我的 cpp 文件代码：

#include "Helper.h"
#include <iostream>

std::vector<float> nums{ 2.4, 65.2, 56.3, 4.6 };

int main() {

    std::cout << convertToString(nums);

}

Answer 1

我认为编译器在编译期间会检查 switch expr。 也许你可以使用一些字符串方法来做到这一点，就像那样
else if (std::is_same<K, char>::value) { result_str.push_back(s); }

else if (std::is_same<K, int>::value) { result_str.append(std::to_string(s)); }

Answer 2

我认为你把事情复杂化了。您可以利用 std::to_string 和类型特征检查器来完成大部分工作：

#include <string>
#include <type_traits>
#include <vector>

template<typename K>
std::string convertToString_helper(K s) {
    //Test from most specific to least to prevent bool and char being converted incorrectly.
    if constexpr(std::is_same_v<K, bool>) {
        return s ? std::string{"true"} : std::string{"false"};
    } else if constexpr(std::is_same_v<K, char>) {
        return std::string{s};
    } else if constexpr(std::is_integral_v<K> || std::is_floating_point_v<K>) {
        return std::to_string(s);
    } else if constexpr(std::is_convertible_v<K, std::string>) {
        return s;
    } else {
        return "Not convertible to a string";
    }
}

template<typename K>
std::string convertToString(std::vector<K>& V) {
    std::string result{};
    for(auto iter = std::cbegin(V); iter != std::cend(V) - 1; ++iter) {
        result += convertToString_helper(*iter) + ", ";
    }
    auto last_iter = std::cend(V) - 1;
    result += convertToString_helper(*last_iter);
    return result;
}

Answer 3

您使用的是浮点向量，因此当编译器编译代码时，它会将模板版本替换为浮点版本，因此switch (s) 行在 switch 语句中使用浮点，至于解决方案，这里是使用字符串流的简化版本

#include <string>
#include <vector>
#include <iostream>
#include <sstream>

std::vector<float> nums{2.4, 65.2, 56.3, 4.6};
std::vector<bool> b{true, false, false};
std::vector<int> i{1,2,3,4,5};
//Converts a vector of any type into a string like this: 2, 5, 6, 3, (Yes the comma stays at the end like that. That can be fixed but it will require huge amounts of code)
template <typename K>
std::string convertToString(std::vector<K> &V)
{
    std::string result_str{""};
    for (auto s : V)
    {
            std::stringstream converter;
            converter << std::boolalpha << s; 
            result_str += converter.str() + ", ";

    }
    return result_str;
}

int main()
{
    std::cout<< convertToString(b)<<std::endl;
    std::cout<< convertToString(nums)<<std::endl;
    std::cout<< convertToString(i)<<std::endl;
}

如果需要，您可以跟进子字符串操作以删除最后一个逗号。