CODEWITHSUNDEEP
mql4metatrader4
hl037_
hl037_

Reputation: 3907

How to return a struct from an imported DLL-function in MQL4?

Is there a way to return a struct from an imported function in MQL4, without having to pass it as a parameter and making a memcpy?

Upvotes: 1

Views: 1112

Answers (1)

user3666197
user3666197

Reputation: 1

Be cautious with any kind of DLL-interfacing, MQL4 Documentation states:

Passing Parameters
All parameters of simple types are passed by values unless it is explicitly indicated that they are passed by reference. When a string is passed, the address of the buffer of the copied string is passed; if a string is passed by reference, the address of the buffer of this string without copying it is passed to the function imported from DLL.

Structures that contain dynamic arrays[], strings, classes, other complex structures, as well as static or dynamic arrays[] of the enumerated objects, can't be passed as a parameter to an imported function.

When passing an array to DLL, the address of the beginning of the data buffer is always passed (irrespective of the AS_SERIES flag). A function inside a DLL knows nothing about the AS_SERIES flag, the passed array is a static array of an undefined length; an additional parameter should be used for specifying the array size.

More glitches apply... Then how to make it work?

Maybe a straight, heterogeneous multi-party distributed processing, which communicates rather results than function calls, independent of all nightmares of maintaining just DLL-imported functions API changes, is a way safer way to go. Using this approach for the last few years and since than have no problems with New-MQL4.56789 string-s that seized to remain string-s and silently started to become struct-s etc.

Worth to know about.

Anyway, welcome and enjoy the Wild Worlds of MQL4 -- may enjoy to click and read other posts on issues in MQL4/DLL integration and/or signalling/messaging in MQL4 domains. Feel free to ask more

Upvotes: 0

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