Comparing Strings in Arduino C++? - c++

Question

I'm currently writing some arduino code for a GUI with with Keypad and 16x2 LCD implementation. Part of my program requires a password to be entered before certain content on the Arduino can be accessed, however I can't seem to figure out how to get my saved password and given input to work properly.
String pswd = "0000";
char* Input(int Length, byte clmn, byte row) {
char output[Length];
int i = 0;
while (i < Length) {
char KeyPress = keypad.getKey();
lcd.setCursor(clmn,row);
if (KeyPress == '0' ||
KeyPress == '1' ||
KeyPress == '2' ||
KeyPress == '3' ||
KeyPress == '4' ||
KeyPress == '5' ||
KeyPress == '6' ||
KeyPress == '7' ||
KeyPress == '8' ||
KeyPress == '9') {
output[i] = KeyPress;
lcd.print(KeyPress);
i++;
clmn++;
lcd.setCursor(i+1,0);
lcd.cursor();}
}
delay(3000);
Serial.println(output);
return output;
}
bool Is_Psswrd() {
bool Passed = false;
char *Test;
String test;
CH2 = true;
while (CH2) {
say("Password: ",0,0);
Test = Input(4, 10, 0);
test = Test;
if (test==pswd) {
Passed = true;
CH2 = false; }
else {
for(int i = 0; i < 3; i++) {
lcd.clear();
say("Incorrect ",0,0);
delay(200); } }
}
return Passed;
}
void setup() {
Is_Psswrd();
}
void loop() {}
I've tried alot of different things for saving, inputting, and checking characters, some more jankier than others. My original plan was to save all variables as char* variables and use the strcmp() function, but that didn't seem to work (strcmp() kept outputting "144") and I learned I needed const char* to make the function work properly. I've given the code I believe is needed to access the issue, but if you need the rest of the code I can paste it.
I am very new to C++. Most of my code is written in Java. Can someone please explain what needs to be done to get two char*/strings to compare in the way I want. I am open to fully rewriting my functions I just need to get this implemented.

Answer 1

If 4 character hard coded "password" is fine, String objects are too much overhead, IMO.
Here's demo code with a 3x4 keypad and a 16x2 display via I2C:
#include <LCD_I2C.h>
LCD_I2C lcd(0x27,16,2);
#include <Keypad.h>
const uint8_t ROWS = 4;
const uint8_t COLS = 3;
char keys[ROWS][COLS] = {
{ '1', '2', '3' },
{ '4', '5', '6' },
{ '7', '8', '9' },
{ '*', '0', '#' }
};
uint8_t colPins[COLS] = { 4, 3, 2 };
// Pins connected to C1, C2, C3
uint8_t rowPins[ROWS] = { 8, 7, 6, 5 };
// Pins connected to R1, R2, R3, R4
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
const byte OFFS =4; // position on lcd
byte pos=0; // 0...3
void setup() {
lcd.begin();
lcd.setCursor(0,1);
lcd.print("PWD:");
Serial.begin(9600);
Serial.println("keypad with lcd");
}
char pwd[5]; // 4 digits + '\0'
bool check (const char* pwd) {
return (strcmp(pwd, "1234")==0);
}
void loop() {
char key = keypad.getKey();
if (key != NO_KEY) {
// Serial.println(key);
lcd.write(key);
if (pos < 4) pwd[pos++] = key;
if (pos == 4) {
bool result = check(pwd);
if (result == false) {
pos = 0;
lcd.setCursor(0,0);
lcd.print("Wrong pwd");
lcd.setCursor(0,1);
lcd.print("PWD: ");
lcd.setCursor(OFFS,1);
} else if (pos == 4) {
lcd.setCursor(0,0);
lcd.print("Hooray ");
lcd.setCursor(0,1);
pos++;
} // else continue writing to bottom line
}
}
}