Adding entry in JsonObject using File object causes corrupted JSON about arduinojson HOT 1 CLOSED

Hi @AcuarioCat,

file.path() returns a const char*, and JsonDocument stores const char* as a pointer and not as a copy like other string types.

The rationale behind this design is that const char* is often used to point to a string literal, which is a read-only memory block. In this case, it's safe to store the pointer directly in the JsonDocument.
Unfortunately, in your case, the const char* points to a temporary string, so it's not safe to store by pointer.

The solution to your problem is to pass any other type of string.
For example, you could cast the const char* to a char* like so:

- jdata["t"] = file.path();
+ jdata["t"] = const_cast<char*>(file.path());

I know it's very unpleasant to use const_cast, but fortunately, it's safe in this case because JsonDocument will not modify the data pointed by the pointer.

If you prefer avoiding the const_cast, you can use a String instead, like so:

- jdata["t"] = file.path();
+ jdata["t"] = String(file.path());

This is clearly a design flaw in the library, and I hope to eliminate it someday.

Best regards,
Benoit

from arduinojson.