読み取り失敗に対処する

Even a good sensor sometimes returns nothing useful. Loose wires, fast polling, or noise can cause a failed read, so plan for it. ⚠️

When a read fails, the library returns NaN, which means Not a Number. It is the sensor's way of saying I did not get a value.

A NaN never equals anything, not even itself. So you cannot just compare it with a normal number to catch the error.

Use the built-in isnan() function to test a reading. It returns true when the value is the failed NaN result.

Always test a reading before you print or act on it. Skipping this check lets bad data slip into your logic unnoticed.

Guard temperature and humidity together, since either can fail. If one is NaN, treat the whole reading as bad and skip it.

When a read fails, print a clear message instead of a value. Future you will thank present you for the helpful note.

A single failure is normal, so do not stop the program. Simply retry on the next loop and the reading usually succeeds.

For a steady display, store the last good reading and reuse it when a read fails. Your screen never shows an ugly blank.

If failures pile up, you may be reading too fast or your wiring is loose. A longer delay and a firm connection often cure it.

Handling errors gracefully is what separates a toy from a real device. Your sensor now survives the occasional hiccup calmly.

A DHT read fails. How should your sketch detect that in code?

You learned that failed reads return NaN, caught them with isnan, warned instead of crashing, and kept your device steady. 🎉