Safety Checks

Hi,

how do you know which safety checks you need to put into your code? I am quite familiar with C++ programming so I can code an EA which does what I want. However, which safety switches to use and where to put them is another matter. Usually I open one of the EAs shipped with MT4 and decided based on their code. Do you just refer to the MQL4 Reference for function errors and then implement checks based on that?

Backtesting shows only so much errors. If you code safety checks solely on that it's very much possible you may encounter some weird error in live trading.

I'm not sure what the term "Safety Checks" means. I am more familar with "Edit Checks", "Error Checks" and "Exception Handling". But I assume this might be a newer way of saying the same thing.

I'm not going to try to address all the aspects of exception handling in MT4 except to say that you need to do the usual check for array bounds and divide by zero. But the way these are handled by default is peculiar to MT4. Basically the program continues to run and the results are undetermined.

The really weak part of MT4 is the means of checking user inputs. What I call Edit Checking. Boolean and Color values can be handled easily as only the proper values are allowed. However for range checking of simple integers, the language is very weak. For instance, if negative numbers are not valid, there is no built in positive value check. Most code that I have seen has no checking at all and the program can produce some useless results. A few programmers try to catch these errors at Init Time by issuing an alert. I have used this myself, but found that users ignored the warning and carried on, so I'm not sure what use the code was.

Others can probably detail their own insights into this subject as I'm sure that many things I haven't covered.

GetLastError
IsConnected
IsDemo
IsDllsAllowed
IsExpertEnabled
IsLibrariesAllowed
IsOptimization
IsStopped
IsTesting
IsTradeAllowed
IsTradeContextBusy


The checkups are pretty useful for the basic running of your EA you can avoid allot of errors by simply making sure that the terminal is connected to the server for example.

as far as safety is concerned you want to make sure that you check your order fills and have a plan B if for some reason an order was not processed correctly. There are some open source libraries that have this error handling, if I remember correctly one was called "order reliable".

Another safety measure might be to add some logic to your system to "avoid" news announcements which can cause volatility.

Also since MT4 can be slow and pricing can be quick, I execute my transactions on incoming ticks then calculate what to do next. as opposed to calculating some complex algorithm then executing a trade.