An error enum in C

Named error codes read better than magic numbers, and map to messages.

typedef enum {
    ERR_OK = 0,
    ERR_NULL_ARGUMENT,
    ERR_OUT_OF_RANGE,
    ERR_OUT_OF_MEMORY,
    ERR_COUNT
} Error;

static const char *messages[ERR_COUNT] = {
    "ok",
    "null argument",
    "value out of range",
    "out of memory",
};

const char *error_message(Error e) {
    if (e < 0 || e >= ERR_COUNT) {
        return "unknown error";
    }
    return messages[e];
}

Error set_stars(int stars, int *out) {
    if (out == NULL) {
        return ERR_NULL_ARGUMENT;
    }
    if (stars < 0 || stars > 3) {
        return ERR_OUT_OF_RANGE;
    }
    *out = stars;
    return ERR_OK;
}

How it works

1. The enum starts at zero for success.
2. A parallel table of strings turns a code into a message.
3. The count member keeps the table and the enum in step.

Keywords and builtins used here

• NULL
• char
• const
• enum
• error_message
• if
• int
• return
• set_stars
• static
• typedef

The run, in numbers

Lines

32

Characters to type

502

Tokens

128

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 73 seconds.

Type this snippet

Step 1 of 2 in Errors & cleanup, step 8 of 11 in APIs, errors & testing.

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