DLL c++ any examples ?

Hi Guys,

could anyone share some DLL sources ? Im trying to write my own but its much easier to understand if i get some examples.

Thanks for your help.

Regards
Tim

here in this forum is a thread with some examples in Free Pascal (use the search function). You should be able to adapt everything that is written there to C++ since both languages are essentially doing the very same things just with a bit different syntax. Pascal examples are expressive and easy to read.

Hi 7,

thanks for your answer - i see this thread already but im trying to learn c.
VB is much easier for noobs like me

Maybe you could help me. I need a simple function that check condition and return 1 if its true or 0 ...
This isnt the exact thing but this would help me very much
Could you write some lines what iam doing wrong ?

1. if you want debugging help you need to tell us what is happening vs what is meant to happen. give some sort of example that we can work-off

2. at first guess just by looking at your code i suspect you are running into massive logic failures due to lack of brackets

e.g. if you do... If (a < b AND c * d >= f OR g != h) { };

you will often find you won't get the booleans you expect as the AND's and OR's and XOR's and NOT's etc often get processed first and screw up what reads one way but is actually processed a different way.

you want... If ( (a < b) AND ((c * d) >= f) OR (g != h) ) { };

and from that you might need, and i would recommend, bracketing even further such as...

IF ( ( (a < b) AND ((c * d) >= f) ) OR (g != h) ) { };

in this example the logic resolves the ab bracket, the cdf bracket, and it then resolves the ab bracket testing AND with cdf bracket, then it can resolve the gh bracket and test the abANDcdf bracket OR gh bracket.

hope that makes some kind of sense. basically, make sure you ALWAYS bracket each section you want resolved else you will find you will read something one way but your code is resolved in a different order.

thanks for your answer. i write my entry point in mql - now i try to export these functions to a dll.
if i try to use the dll in state of the mql code - the backtests are crazy different ... so something isnt work correctly......

i will try to use more brackets
but i have a 2 other questions - is it correct that i use "const double"?
is it right how a negate the values like (-cci1val) is this possible if i use "const double"

And is it possible that i could Print something from inside the DLL to MT4 that i could check the values against the mql code ?
maybe this could help me with debugging..

Thanks for our help !

i have done little dll programming and it's been awhile since i've coded anything significant...

but const is fine because you are not actually assigning new values to anything. this is the whole point of const in that the compiler can check that you aren't accidentally writing somewhere a new value to a value you don't want changed.

double is also fine because it is a signed type (i.e. can have negative values).

in terms of printing from the dll... the easiest thing to do by far is simply write a log into a textfile from within your function, and then later go back and check the values by hand.

i'd write to file firstly the values passed to the function, and then on a separate line before returning from the function write the value of "back". if from the log you can see something doesn't make sense then you can start working-out the logic test in your code by hand with the values passed in the log file to see what you are expecting and can then see where you have coded it wrong.

I would do "printing" from the DLL via OutputDebugStringA() (this is from the Windows API, exported by kernel32.dll)

You can then just use a tool like DebugView (SysInternals) to view this output in realtime or filter it or log it to disk.

Many many thank for your efforts !
The Debugging with Debugview seems to work if i use a test string. GREAT !

Could you send me a short info how i could the const doubles
concatenate and convert it to one string that i could use this string for the debug function ?

google and guessing suggests Cstr(doublevar1) + Cstr(doublevar2) etc

do you have a vb help file in your IDE? i would think it'd have these type of functions listed somewhere accessible since it's fairly useful and bound to be used a lot.

This must be answered by somebody who knows C++. There should be functions for such conversions in the standard libraries, you just need to use the documentation to find out which ones and how to use them.

If you are new to such low level programming (I consider messing around with memory allocation and string copying as low level, at least for a beginner) you should really not start with C or C++. If you don't have a hard requirement for using C++ (an existing project is written in C++ or something like that) then there is absolutely no reason to torture yourself with this bizarre language. You should instead learn Pascal (Free Pascal), It is far more fun programming in Pascal and you can do exactly the same high performance low level stuff, just about twice as easy and with a much cleaner syntax.

holy crap this isn't vb. my bad. i don't even know vb, which shows lol.

pascal is definitely not a bad choice... but i say that as someone who is a delphi coder by hobby . saying THAT, i've coincidentally been looking into freepascal and lazarus (and GLscene) just the last few hours which is freaky, and if i get motivated i might have to just crack into these since i don't have delphi installed on this win7 machine yet and it's such an old version i have on disc that something a little more fresh is in order.

if you get into pascal you need to be aware it often handles library calls in a different order unless you specify stdcall in the procedure/function declaration, but this is usually highlighted in any help file relating to pascal and dll's anyway so you won't forget.

This code worked fine wih the example from MT4 and vc++ in combination with debugview !
Many thanks for all your help.

well done. would have been heaps easier in pascal though

did you work-out what was going wrong with it in the first place, or was it just how to get it compiling that was the problem?

nope - but now i could see what happens when i call the function.
will write again after i finished the debugging ..

Regards
Tim

now write a function, call it log() that takes a string and a double argument, does the conversion and concatenate it all to a debug message, then you can conveniently use it as a replacement for Print() in the following manner:

You can also export this function so you can also use it from mql4 to have all your debug output in one place.

i try and try and try ....

i split all the AND condition to many ifs
and another "if" for the OR condition

the crazy thing is that it works very close together - but if i use the DLL function in state of mql code it opens sometimes a order when the mql wouldnt open a trade - not many but happen... and so the results are very different ...

The main thing that i could see in the debugview that it rounds the doubles a little bit different 0.8675 mql could be 0.86745 in the dll
i will try to round the doubles same as MQL digits - maybe this could help.

what a round function could i use ?

Thanks again !

Hi again, i found something to round


I could call this function from mt4 - but not inside the dll ?
what i have to do ?

Thanks for your help !!

it sounds to me like you really are a beginner coder. like, as in, really only just beginning.

learning c++ or any language for use in something that interests you, such as mt4 indicator / ea interaction, is probably just as good as any other motivation to learn... however, you should hit-up some dead-set beginner c++ pages to learn the structure and methodology of the language.

unlike trading where every clown says all you need to do is follow the trend, just trade, use x, use y, blah blah, it will be fine with the right psyche, blah blah... with coding you get back what you put in, directly. learn what you want to do and you will be able to do it, period. writing code is like wielding a knife. some languages are 'sharper knives' than others and can do more damage, or rather, will let you do more damage. you need to learn how to properly wield the knife / language, and from this you will have capabilities to do things you previously had no idea how to do.

c++ is gonna hurt you though to start with. it's not as simple to just pick-up and go as other languages. no matter which way you go, once you have learned one real language properly you will understand how to go about things in other languages, and only need to learn a new syntax. it's like learning new verbal languages... once you have been exposed to nuances of a new verbal language your mind is open to the same in others and things make similar sense all-round.

google c++ tutorials.

Hi,

thanks for your answer. I know c/c++ isnt very easy for a beginner - vb is much easier but now its c time for me !

I tried serveral things now to find out what is wrong with my dll function ... and all i could say ... "nothing is wrong"

I test the following today - i round the indicator values before i call the dll function to 5 Digits ( exactly as in the dll ) i get the same results !
So im thinking nothing is wrong because mql does the same as the dll code if the doubles are rounded to 0.00000

Now my question - how is mql rounding the doubles ? is there anything to read about it ? is mql cutting or really rounding ? how accurate ( numbers after point ) is mql using ?

Many thanks for your help.
Tim

interesting. don't know. maybe do a find for 'normalize' as well as 'round' and see if anywhere in the code you have either of these pop up that you don't realize is in there. very odd.