Discussing the article: "How To Debug MQL5 Code in MetaEditor"
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Check out the new article: How To Debug MQL5 Code in MetaEditor.
This article is a practical walk-through of the MetaEditor debugger using a rolling z‑score indicator with two planted bugs: an off‑by‑one array access and a silent wrong‑denominator variance. We show how to set breakpoints, step through code, read the call stack, and inspect values in the Watch window. You will learn a repeatable method to catch both crashing index errors and tiny numerical biases that charts cannot reveal.
In the previous article I put a small indicator under the MetaEditor profiler and let two columns of numbers tell me where its time was going. The profiler answers one question well: where is this program slow? It has nothing to say about a different and often costlier question, the one where the program is fast enough but simply wrong. A line draws smoothly, the terminal reports no error, and yet the values it plots are quietly incorrect. For that class of problem MetaEditor ships a separate tool, the debugger, and this article is a practical walk-through of it, in the same spirit as the profiler piece: the focus is the tool, not the strategy.
To keep that focus, I use the same small example as before, a rolling z-score, but this time I write it with two deliberate bugs planted in it. I put them there on purpose, so that there is something concrete to find and so each bug exercises a different part of the debugger. The first is an off-by-one in a window loop, the kind of index mistake that reads one element past the edge of an array. The second is quieter and more instructive: a wrong denominator in the variance that never crashes anything, plots a perfectly plausible line, and is wrong on every bar by an amount too small to see on a chart. One bug you can trigger by accident; the other you can only find by reading the number itself.
The goal is not this indicator and it is not a tour of every menu item. It is the working method: how to set a breakpoint, how to step through code one line at a time, how to read variable values in the Watch window at the exact moment they go wrong, and how to follow the call stack back to the caller. Once you can drive the debugger, you can point it at your own indicators, libraries, and Expert Advisors and find out, instead of guessing, why they behave the way they do.
Author: Shahzaib