Comparing Char to String

Question

I am currently doing a college project and most of my background comes from JS & Python. I have an Arduino that is receiving data and using ArduinoJSON to take in settings and deserialize them. I have it set up that the setting is a const char* setting. Which can contain a range of data types (mostly int or bool). But I am focused on trying to get a bool value from the char.

setting = doc["setting"];
if (setting == "true") {
  test = true;
} else if (setting == "false") {
  test = false;
}

I tried the above with no luck. I also tried converting the char to a string but with no luck. I also tried to use the .compare() function with no luck either. What would you guys recommend?

`==` is not the correct way to compare C strings. Use `strcmp` or use C++ `std::string`. — kaylum, Apr 15 '21 at 22:59
If you want to compare null terminated strings, use the appropriate function, like `strcmp()`. As an aside, what should happen with `test` if neither test passes? Will it be indeterminate? — Deduplicator, Apr 15 '21 at 23:00

score 1 · Accepted Answer · answered Apr 15 '21 at 23:01

With const char*, the == operator will compare the pointer values rather than the text value (which will generally always be different since the data is stored in different locations). You could change it to:

if (strcmp(setting, "true") == 0) { test = true; }
else if (strcmp(setting, "false") == 0) { test = false; }

instead to get things working. Alternatively you could cast the setting to a String before doing the comparison and that should work as well:

String setting = String(doc["setting"]);
if (setting == "true") { test = true; }
else if (setting == "false") == 0) { test = false; }

Comparing Char to String

1 Answers1