Using std :: error_code with non-integer values

Question

I am writing a library and want to return error codes whenever the remote system returns an error. The problem is that they are identified by strings, for example, "0A01", and also contain a message, and the error code requires an integer value.

What is the best way to implement an error code with all the functionality provided std::error_codebut using strings as a value? How to add an external error line to std::error_codeor std::error_category?

Answer 1

As mentioned in the comments, you should know the error codes that can be received from the remote server. std::stringthat you get from a remote server contains 2 parts, as you said,

The problem is that they are identified by lines, for example, "0A01", and also contain a message, and the error code requires an integer value.

Since you did not share the format of the error message, I am not adding code to grind it, divide the line into 2 parts,

• Error code
• Error message

Now you can convert the type of error code std::stringin the intusing std::stoi(error_code), so let's say

int error_code_int = std::stoi(string_to_hexadecimal(error_code));

And for std::error_category, which serves as the base class for our custom error messages, do this,

std::string message_received = "This is the message which received from remote server.";

struct OurCustomErrCategory : std::error_category
{
  const char* name() const noexcept override;
  std::string message(int ev) const override;
};

const char* OurCustomErrCategory::name() const noexcept
{
  return "Error Category Name";
}

std::string OurCustomErrCategory::message(int error_code_int) const
{
    switch (error_code_int)
    {
    case 1:
        return message_received;

    default:
        return "(unrecognized error)";
  }
}

const OurCustomErrCategory ourCustomErrCategoryObject;

std::error_code make_error_code(int e)
{
  return {e, ourCustomErrCategoryObject};
}

int main()
{
    int error_code_int = std::stoi(string_to_hexadecimal(error_code));  // error_code = 0A01
    ourCustomErrCategoryObject.message(error_code_int);
    std::error_code ec(error_code_int , ourCustomErrCategoryObject);
    assert(ec);

    std::cout << ec << std::endl;
    std::cout << ec.message() << std::endl;
}

The output for the above working example

Error Category Name : 0A01
This is the message which received from remote server.

string_to_hexadecimal() .

, .

1:

,

, . std::error_category?

, std::error_code::assign std::error_code::error_code int error_category. , , std::error_code .

, , std::error_code error_category , , ?

std::error_category , :

std::error_category .

, , struct std::error_category

struct OurCustomErrCategory : std::error_category

, -, struct ,

struct OurCustomErrCategory : std::error_category
{
    std::string message_received;
    OurCustomErrCategory(std::string m) : message_received(m) {}

    const char* name() const noexcept override;
    std::string message(int ev) const override;
};

, ,

const OurCustomErrCategory ourCustomErrCategoryObject("This is the message which received from remote server.");

Answer 2

error_code. , . , :

http://blog.think-async.com/2010/04/system-error-support-in-c0x-part-4.html