importing DLL functions

[Bogdan Caramalac]

I am having trouble importing DLL functions that expect a pointer to a string.

Something like this:

#import "user32.dll"
    int GetWindowTextA(int hwnd,string &lpstring,int nMaxCount);
#import

So, after finding out the hwnd, I call the function and pass the lpstring, after I previously initialize it with 50 spaces... and I get it the same out of the function (of course with a MaxLength of 30 (should have used GetWindowTextLength, but I knew exactly to which window the handle belongs :))  ) )

The & shouldn't instruct MetaTrader to pass the internal pointer, which is then linked tot the represented variable ?

[Rashid Umarov]

Try this way

#import "user32.dll"
    int GetWindowTextA(int hwnd,string & lpstring,int nMaxCount);
#import
 
....
string Text[1]={""};
int  valueInt=GetWindowTextA(handlewnd,Text[0],MaxCount);
Print(Text[0]);

See also 'Crash в "About"' and 'Скрипт "Каталог программы"'

[Bogdan Caramalac]

Thanks Rosh, that worked! Only difference is that , for correct retrieval, MaxCount must be GetWindowTextLengthA(handle)+1 instead of GetWindowTextLength(handle). Don't know why it requests an extra char.

[Rashid Umarov]

You're welcome.

[Bogdan Caramalac]

STRANGE!

We both made a mistake. Even me, when I wrote the example.
By accident, I used the & operator when writing my post, as It is technically true, but my example works WITHOUT it. If i put that operator there, the compiler rejects the effective parameter pass when calling the function, as being in "incompatible types" situation. Looks fishy for the compiler to do that...

[Slava]

There is side effect with passing strings as reference. See https://www.mql5.com/en/forum/46512 my answer at 28.03.07 10:00

[[Deleted]]

Hi, I tested import 2 *.dll to my code, but compiler return error message: double quotes needed

I am not author *.dll files. What do you mean error message? If possible the same name any function inside dll?

[William Roeder]

1. Why are you replying to a five year old post?
2. No mind-readers here. Post your code.

3. Play video	Please edit your post. For large amounts of code, attach it.