How to Resolve an MQL Syntax Error
Inspect the Error message, then locate & fix the problem
The VTS output tab will show the exact MQL syntax error:
Although this shows the exact location of the error in the MQL file, this information may not be very helpful, especially with a large system.
To find out more, click the Editor button to launch the MetaEditor. Then press F7 in the MeteEditor – this will build the EA. The same error message is shown in the MetaEditor’s Error tab:
When you double-click the error, it will bring you to the exact location of the error in the MQL file.
In this case the error is associated with the MQL Variable named Variable1
Now you can inspect that Element on your VTS drawing:
The assignment field of the Variable1 Element contains a semi-colon (;). This is not valid MQL syntax, so it causes the MQL build to fail. Changing the semi-colon to 0 (zero), or some other value will fix the error.
Every error is a little different , but the objective is the same: find the general location of the error and then make changes to see if the error is resolved.
Important Note: The first time you click the Editor button in VTS, the MetaEditor is launched and the Expert Advisor for the current VTS system is loaded into the MetaEditor. But, and this is significant, if you make changes to your VTS drawings and rebuild by clicking the Build button, the MQL file in the MetaEditor will not be refreshed. You need to close the file in the MetaEditor and then reopen it to see the latest changes. There is simply no facility that VTS can use to instruct the MetaEditor to reload a file. We had a sloppy work-around in a previous version of VTS, but changes were made to the MT platform (around build 400) that caused the work-around to break.
- This is a handy trick: If an Element is not connected (using a link) on the VTS drawing pad, it will not be included in the MQL code and therefore will not be built. So you can temporarily remove the links to/from an Element and re-build. If the error is gone, then the problem was caused by the excluded Element. Also, you can remove all links – just connect the Start Element to an End Element, and rebuild as you add each Element back to the drawing one at a time.
- You can get more information about the MetaEditor in this post.
- We offer a free email MQL course. Through a series of emails, it teaches you how to program MetaTrader4 Expert Advisors. No strings attached, just a bunch of emails spaced out over a few weeks.
- I’ve written an ebook on how to learn MQL: MQL For Traders