How convert a string to the value of a const with the same name?

Using Arduino Programming Questions
#1

For a domotica project I want to emulate a Bluetooth keyboard. The domotica bridge can sent strings of data to a ESP32… The library has a bunch of key’s declared as const. Like:

const uint8_t KEY_UP_ARROW = 0xDA;
const uint8_t KEY_DOWN_ARROW = 0xD9;
const uint8_t KEY_LEFT_ARROW = 0xD8;
const uint8_t KEY_RIGHT_ARROW = 0xD7;
const uint8_t KEY_BACKSPACE = 0xB2;
const uint8_t KEY_TAB = 0xB3;
const uint8_t KEY_RETURN = 0xB0;
const uint8_t KEY_ESC = 0xB1;
const uint8_t KEY_INSERT = 0xD1;
const uint8_t KEY_DELETE = 0xD4;
const uint8_t KEY_PAGE_UP = 0xD3;
const uint8_t KEY_PAGE_DOWN = 0xD6;
const uint8_t KEY_HOME = 0xD2;
const uint8_t KEY_END = 0xD5;

(And so on…)

How can I convert an incoming string like “KEY_UP_ARROW” to the const? Or do I really need to create long if else solution like this:

if (strcmp(incomingString, "KEY_UP_ARROW")==0) {
    result = KEY_UP_ARROW;
}
else if (strcmp(incomingString, "KEY_DOWN_ARROW")==0) {
    result = KEY_DOWN_ARROW;
}

Surely there must be an more elegant and easier way.

#2

Rather than send a string, you could always just send the key value directly as a single byte and avoid all the compares. Or maybe send the hex value as ascii (e.g. "DA" ) and then convert that to its actual value.

#3

Yes, but I want to keep the user-side (on the Domotica controller) readable and user friendly.

#4

Create an array of structs in progmem to hold the mapping and loop through it to look up the 0xDA value when you have received “KEY_UP_ARROW”.

#5

satoer:
do I really need to create long if else solution
Surely there must be an more elegant and easier way.

A lookup table and 'for' loop.

#6

Thanks. That seems a neater solution.

#7

It's easy to change a bunch of const declarations to lookup array initializers with a text editor:

const uint8_t KEY_UP_ARROW = 0xDA;
const uint8_t KEY_DOWN_ARROW = 0xD9;
const uint8_t KEY_LEFT_ARROW = 0xD8;

Change " = " to "", ":

const uint8_t KEY_UP_ARROW", 0xDA;
const uint8_t KEY_DOWN_ARROW", 0xD9;
const uint8_t KEY_LEFT_ARROW, 0xD8;

Change ";" to "},":

const uint8_t KEY_UP_ARROW", 0xDA},
const uint8_t KEY_DOWN_ARROW", 0xD9},
const uint8_t KEY_LEFT_ARROW, 0xD8},

Change "const uint8_t " to " {"":

  {"KEY_UP_ARROW", 0xDA},
  {"KEY_DOWN_ARROW", 0xD9},
  {"KEY_LEFT_ARROW, 0xD8},

Add some trim around that and you have:

struct {char *name, uint8_t value} LookupTable[] = {
  {"KEY_UP_ARROW", 0xDA},
  {"KEY_DOWN_ARROW", 0xD9},
  {"KEY_LEFT_ARROW, 0xD8},
};
#8