Which folder should I place .mqh files to be recognised by my EA?

I created some .mqh files and left them in the Include folder (not a subfolder of the Include folder). I tried calling a class from the .mqh in my Expect Advisor but I keep getting a “undeclared identifier” error. Where should I place my .mqh files to be recognised by my Expert Advisor?

Most of my .mqh files are in MQL5\Include.

I have some in a sub-directory of MQL5\Expert.

Shouldn’t matter so long as you have your #include lines correct in the calling .mq5 file.

What should the #include path be?

Depends upon where the .mqh file is.

These are all valid. I know this because I just copied out of a working EA. As you can see, I mix and match angle brackets with double quotes as needed.

And note that you can include .mq5 files as well.

#include <clsTimeSeriesData.mqh>
#include <clsTradeMetrics.mqh>
#include <clsOkToTrade.mqh>
#include "..\..\libraries\clsMoneyManagement.mq5"
//#include "..\..\libraries\clsInternalAverages.mq5"
#include <clsShowStatistics.mqh>
#include "TimeSeries.mqh"
#include "RSquare.mqh"
#include <clsStrategy.mqh>
#include <clsRange.mqh>
Read this link for specific details: https://www.mql5.com/en/docs/basis/preprosessor/include

Thanks, that solves it.