Both 3x and 4 fail to compile jsonlib.cpp in Arduino 1.8.1.3 and 2.0.0-beta.5

[hylioja]

Both versions (3.x and 4) fail with this error message in both Arduino 1.8.1.3 and 2.0.0-beta.5:

sketch\src\jsonlib\jsonlib.cpp: In function 'String jsonExtract(String, String)':
sketch\src\jsonlib\jsonlib.cpp:75:34 error: 'std:string' has not been declared
if (json.indexOf(name) == std::string:npos) return json.substring(0,0);

[easytarget]

That looks like a really fundamental corruption in your ESP arduino core install. The std:string stuff is included via Arduino.h and a core part of all arduino toolchains.

• Upgrade to the latest Arduino IDE, currently 1.8.15
• Reinstall the ESP32 core: at v 1.0.6: https://github.com/espressif/arduino-esp32#installation-instructions
• Try the simple strings test example at: examples -> built-in examples -> 08.Strings -> StringLength with the correct ESP32 board selected in the boards list. This should compile correctly.

There is nothing to 'fix' in my code for this, you need fix whatever is wrong in your toolchain.

[blurfl]

I too am seeing this issue when using the alpha preview version of the ESP arduino core. Dropping back to the 1.06 release compiles correctly. I find that the simple strings test example compiles correctly with the alpha (maybe because it does not call std::string::npos ?) At any rate the issue with std::string::npos seems to lie with the alpha version of the core.

For now, to keep working with the alpha I work around the issue by editing src/jsonlib.cpp line 76 to avoid the issue:

  if (json.indexOf(name) == name.length()) return json.substring(0,0);

[easytarget]

https://www.cplusplus.com/reference/string/string/npos/
It's a constant that represents 'No Position'

So the conditional (json.indexOf(name) == std::string:npos) is basically testing to see if name exists in the input, I'm not convinced your modified line will work reliably.

Looks like this needs to be taken up as a issue with the ESP alpha.

[easytarget]

I just submitted espressif/arduino-esp32#5342

However, I'm pretty sure this is now the intended behaviour for the ESP core, it makes it consistent with other cores, eg neither the esp8266 or the official Arduino cores support std::string in this way either. String support in Arduino-land is, by convention, a subset of the full std::string package.

So I've done a proper fix in the code to remove the std::string reference and ensure this is not a problem going forward.