Converting Enum Error Code To String - c

Question

In a project I am working on, I have defined a basic enum to store a list of the possible errors the application could encounter. However, I would like to find a way to return a string describing the error.
Here's the enumeration I'm using:
enum _library_results_enum{
LIB_SUCCESS = 1,
LIB_FAIL,
LIB_NULL_PARAM,
LIB_MALLOC_ERROR,
LIB_TIMEOUT,
LIB_CONNECTION_CLOSED
}
If a function returns a result other than LIB_SUCCESS, then ideally I would like to be able to just say:
printf("Error Description: %s\n", ERROR_DESCRIPTIONS[RESULT]);
To handle that I would imagine I need a static const *char[] to house an array of all descriptions. However, the enum values do not start at zero (0) and eventually I might add some negative values to this enum. Thus, using an array of strings isn't really an option. What else could I do to handle this?
I have considered just creating a function which uses a switch statement to return back a description. However, this is really just a fallback solution if there is not a better option.
Edit: To better clarify, what I need is a way to associate result codes within an enumeration to a string describing them.

Answer 1

Your proposed fallback solution of a function that returns strings for each of the discontinuous error code looks like a good solution to me.
A nice solution to keep enum and messages lined up and to ensure that each enumerated value has its message are X macros. (I now see that Weather Vane has beaten me to this answer by posting a link.)
Here's how that might look applied to your problem:
#include <stdlib.h>
#include <stdio.h>
#define ERROR_CODES(X) \
X(0, LIB_SUCCESS, "No error at all!") \
X(10, LIB_FAIL, "An error occurred") \
X(20, LIB_NULL_PARAM, "Illegal null param") \
X(30, LIB_MALLOC_ERROR, "Allocation failed") \
X(40, LIB_TIMEOUT, "Connection timed out") \
X(-5, LIB_CONNECTION_CLOSED, "Connection closed") \
#define ERROR_ENUM(ID, NAME, TEXT) NAME = ID,
#define ERROR_TEXT(ID, NAME, TEXT) case ID: return TEXT;
enum {
ERROR_CODES(ERROR_ENUM)
};
const char *error_msg(int code)
{
switch (code) {
ERROR_CODES(ERROR_TEXT)
}
return "Unknown error";
}
int main()
{
puts(error_msg(LIB_TIMEOUT));
puts(error_msg(LIB_CONNECTION_CLOSED));
puts(error_msg(LIB_SUCCESS));
return 0;
}