返回char *而不是字符串 [英] Returning char * instead of string

问题描述

如何在C ++ 11中更正以下代码:

How may I correct the following code in C++11:

    const char *what() const noexcept override {
        return "Mtm matrix error: Dimension mismatch: (" + std::to_string(mat1_height) + "," +
               std::to_string(mat1_width)
               + ") (" + std::to_string(mat2_height) + "," + std::to_string(mat2_width) + ")";
    }

如您所见，我返回的是 string 而不是 const char * ，但这不会自动转换吗?以及如何解决?

As you can see I'm returning string instead of const char* but won't that be converrted automatically? and how to fix that?

注意:我想要的东西看起来像c ++代码，而不是c，例如，使用 sprintf

Note: I want something to look like c++ code and not c using sprintf for example

推荐答案

但是那不会自动转换吗?

but won't that be converrted automatically?

否.

以及如何解决?

将字符串存储为成员，然后在 what 中调用 c_str().示例:

Store the string as a member, and call c_str() in what. Example:

struct descriptive_name : std::exception {
    std::string msg;

    descriptive_name(
       int mat1_width,
       int mat1_height,
       int mat2_width,
       int mat2_height)
         : msg(
           "Mtm matrix error: Dimension mismatch: ("
           + std::to_string(mat1_height)
           + ","
           + std::to_string(mat1_width)
           + ") ("
           + std::to_string(mat2_height)
           + ","
           + std::to_string(mat2_width)
           + ")"
           )
    {}

    const char *what() const noexcept override {
        return msg.c_str();
    }
};

甚至更好:从 std :: runtime_error 继承，不要覆盖 what ，并使用消息字符串初始化基类.示例:

Even better: Inherit from std::runtime_error, don't override what, and initialise the base class with the message string. Example:

struct descriptive_name : std::runtime_error {
    descriptive_name(
       int mat1_width,
       int mat1_height,
       int mat2_width,
       int mat2_height)
         : std::runtime_error(
           "Mtm matrix error: Dimension mismatch: ("
           + std::to_string(mat1_height)
           + ","
           + std::to_string(mat1_width)
           + ") ("
           + std::to_string(mat2_height)
           + ","
           + std::to_string(mat2_width)
           + ")"
           )
    {}
};

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