Pointer to pointer comparision breaks when while(1) removed - why? - c++

Question

Trying to build a menu system but running into some issues with pointers - which I don't have much experience with.
I don't understand why removing the while(1) makes the comparison fail between mainmenu_table[1][i] == &option6 but for some reason it does.
What am I doing wrong? Using visual studio and an atmega328p. Thanks
Serial output with original code:
Serial begins
MeNu6
MeNu6
Starting compare loop
it worked
Serial output with while(1) removed.
Serial begins
MeNu6
MeNu6
Starting compare loop
the end
Original code (with while(1) included)
const char option1[] PROGMEM = "Menu1";
const char option2[] PROGMEM = "MEnu2";
const char option3[] PROGMEM = "MeNu3";
const char option4[] PROGMEM = "Menu4";
const char option5[] PROGMEM = "MEnu5";
const char option6[] PROGMEM = "MeNu6";
const char option7[] PROGMEM = "menu7";
const char* const submenu1_table[] PROGMEM = { option1, option2, option3 }; // array of pointers to chars stored in flash
const char* const submenu2_table[] PROGMEM = { option4, option5, option6, option7 };
const char** const mainmenu_table[] PROGMEM = { submenu1_table, submenu2_table }; //array of pointers to pointers to chars in flash
// The setup() function runs once each time the micro-controller starts
void setup()
{
Serial.begin(9600);
delay(100);
Serial.println("Serial begins");
Serial.println((const __FlashStringHelper*)(mainmenu_table[1][2])); // prints "Menu6" as expected
Serial.println((const __FlashStringHelper*)option6); // also prints "Menu6"
Serial.println("Starting compare loop");
for (int i = 0; i < 4; i++) {
if ( mainmenu_table[1][i] == &option6 ) { //
Serial.println("it worked");
while (1); // COMMENTING THIS OUT MEANS DOESN'T COMPARE SUCCESSFULLY.
}
}
Serial.println("the end");
}
// Add the main program code into the continuous loop() function
void loop()
{
}

Answer 1

According to Arduino description of PROGMEM, you cannot access the data through pointers to it directly as with plain pointers. You need to use the proper macros/functions to access the data.
In your code, the pointer tables themselves are located in the PROGMEM, so, to extract the individual pointers, you are supposed to do something like:
const char** submenu = (const char**)pgm_read_word(&(mainmenu_table[1]));
const char* option = (const char*)pgm_read_word(&(submenu[i]));
if (option == option6) {
//...
This code is based on the string table example from the first link.