Possible to convert list of #defines into strings

Question

Suppose I have a list of #defines in a header file for an external library. These #defines represent error codes returned from functions. I want to write a conversion function that can take as an input an error code and return as an output a string literal representing the actual #define name.

As an example, if I have

#define NO_ERROR 0
#define ONE_KIND_OF_ERROR 1
#define ANOTHER_KIND_OF_ERROR 2

I would like a function to be able to called like

int errorCode = doSomeLibraryFunction();
if (errorCode)
    writeToLog(convertToString(errorCode));

And have convertToString() be able to auto-convert that error code without being a giant switch-case looking like

const char* convertToString(int errorCode)
{
    switch (errorCode)
    {
        case NO_ERROR:
           return "NO_ERROR";
        case ONE_KIND_OF_ERROR:
           return "ONE_KIND_OF_ERROR";
        ...
     ...
...

I have a feeling that if this is possible, it would be possible using templates and metaprogramming, but that would only work the error codes were actually a type and not a bunch of processor macros.

Answer 1

I normally do it the giant switch case way, although I make it somewhat easier with:

#define STR(code) case code: return #code
switch (errorCode)
{
    STR(NO_ERROR);
    STR(ONE_KIND_OF_ERROR);
}

This is a good question, I'm interested to see what better ways people have

Answer 2

You are correct. There's no way to recover preprocessor-defined identifiers at runtime (unless you can read the source, but that's cheating). You would be better off creating a constant array of the names and indexing it with the error code (with proper boundary checks of course) - it should be quite easy to write a script to generate it.

Answer 3

take a look at boost preprocessor. You could create list/array/sequence of code pairs:

#define codes ((1,"code1"))((...))

#define code1 1
...

// then use preprocessor FOR_EACH to generate error handlers

relevant link:

http://www.boost.org/doc/libs/1_41_0/libs/preprocessor/doc/ref/seq_for_each.html

http://www.boost.org/doc/libs/1_41_0/libs/preprocessor/doc/ref/tuple_elem.html