How to return an error message string

Question

I have written a driver in C++ for a peripheral device and in short, there is a number of errors that can occur during interaction. I have defined error codes for all the possible errors. I want to write a method that enables the user to query the meaning of error code.

Bear in mind that I have a total of 17 possible errors. The corresponding messages are of varying lengths.

I have solved it with a function that accepts the error code and returns a string with the error message. The function uses the error code to loop through a switch case routine each case returning a different error message as shown below.

std::string getErrorMessage(int errorCode)
{
    std::string errorMessage = "no error" ;

    switch(errorCode) {
    case 0:
        errorMessage = "no error" ;
        break ;
    case 10:
        errorMessage = "there is a network error" ;
        break ;
    case 40:
        errorMessage = "there is a network or protocol error" ;
        break ;
    default:
        errorMessage = "unknown error" ;
    }

    return errorMessage ;
}

This function works, but it's not a "pretty" solution. Does anyone have any ideas or suggestions for a better solution?

I see that this is the least of your problems, but you might spend a minute thinking about internationalization, i.e. different error messages for different locales. Far too much software out there doesn't give a damn... — DevSolar
– DevSolar, Commented Oct 29, 2013 at 15:17
why not to use standard system error codes, and get the description with strerror(errCode)? — SHR
– SHR, Commented Oct 29, 2013 at 15:24

tristan · Accepted Answer · 2013-10-29 15:18:03Z

5

If your error number is not large, using a table is more efficient

char *error[SIZE] = 
 {
   [0] = "NO error",
   [10] = "there is a network error",
   [40] = "there is a network or protocol error",
    ....
}

You need some defensive check to make sure the error number is in range.

This is how glibc implments strerror() as I can recall.

answered Oct 29, 2013 at 15:18

tristan

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LihO · Accepted Answer · 2013-10-29 15:19:46Z

4

You could use std::map<int, std::string> for mapping error messages to according codes:

std::string getErrorMessage(int errorCode)
{
    static std::map<int, std::string> codes;
    static bool initialized = false;
    if (!initialized) {
        codes[0]    = "No error.";
        codes[10]   = "Network error.";
        codes[40]   = "Network or protocol error.";
        initialized = true;
    }
    if (codes.count(errorCode) > 0)
        return codes[errorCode];
    return "Unknown error.";
}

answered Oct 29, 2013 at 15:19

LihO

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Comments

James Kanze · Accepted Answer · 2013-10-29 15:17:17Z

3

If your error codes are sparse, the switch is probably the best solution. If you can make them dense, however, then you can just put the error messages in a table and use the error code to index into it.

answered Oct 29, 2013 at 15:17

James Kanze

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Raxvan · Accepted Answer · 2020-01-10 08:28:29Z

2

You can use a map to store the errors and initialize them in one place for everyone to see:

std::map<int,std::string> error_codes;
void init_codes()
{
    error_codes[1231] = "error 1";
    error_codes[121231] = "error 2";
    error_codes[131231] = "error 3";
    error_codes[135] = "error 4";
    error_codes[10] = "error 5";
    error_codes[0] = "error 6";
}

std::string get_error(const int e)
{
    auto i = error_codes.find(e);
    if( i != error_codes.end() )
    {
        //error was found
        return (*i).second;
    }
    else
    {
        return "Unknown error";
    }
}

edited Jan 10, 2020 at 8:28

answered Oct 29, 2013 at 15:19

Raxvan

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1 Comment

Raxvan Over a year ago

As a side note the error codes can be even read from a file and added to the map

Ferruccio · Accepted Answer · 2013-10-29 15:35:01Z

1

If the error message are fixed, you are probably better off returning a const char*. It's a lot more efficient, involves no memory allocation and is convertible to a std::string if necessary.

const char* getErrorMessage(int errorCode)
{
    switch (errorCode) {
        case 0: return "no error";
        case 10: return "there is a network error";
        case 40: return "there is a network or protocol error";
        default: return "unknown error";
    }
}

answered Oct 29, 2013 at 15:35

Ferruccio

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