.def file vs. __declspec(dllexport) | Forex Factory

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.def file vs. __declspec(dllexport)

  • #1
  • First Post: Sep 20, 2011 2:50pm Sep 20, 2011 2:50pm
hi,
I'm a bit confused about the
.def files and #define MT4_EXPFUNC __declspec(dllexport)

I know I can use .def files and it works.

But did I understood when I define something like

PHP Code
#define MT4_EXPFUNC __declspec(dllexport)
I can skip the .def file.

http://msdn.microsoft.com/en-us/libr...=vs.80%29.aspx

Did I misunderstand this?

Anyone knows how to set that correctly in Visual Studio Express 2008 C++

Thanks a lot.
__Thanks__ MJ
  • #2
  • Sep 20, 2011 6:44pm Sep 20, 2011 6:44pm
from MQL reference:
Quote
Functions imported from DLL into an mql4 program must provide linkage convention accepted for Windows API functions. To provide such a convention, the key word __stdcall specific for compilers of Microsoft(r) company is used in the source codes of programs written in C or C++ language.

then use def file to avoid the function name from being decorated.
  • #3
  • Sep 20, 2011 9:24pm Sep 20, 2011 9:24pm
We use the def file to write the functions name that we want the outside world (metatrader in our case) to see and use.

If you didn't write the function name un the def file you will get very strange function name.

Please read my article about:
Create your own Metatrader extension (dll)

Quoting M_j
hi,
I'm a bit confused about the
.def files and #define MT4_EXPFUNC __declspec(dllexport)

I know I can use .def files and it works.

But did I understood when I define something like

PHP Code
#define MT4_EXPFUNC __declspec(dllexport)
I can skip the .def file.

http://msdn.microsoft.com/en-us/libr...=vs.80%29.aspx

Did I misunderstand this?

Anyone knows how to set that correctly in Visual Studio Express 2008 C++

Thanks a lot.


Stop asking ChatGPT for broken MQL code. VisualMQL it instead.
  • #4
  • Sep 21, 2011 3:07am Sep 21, 2011 3:07am
Thanks guys.

Maybe I phrased my question wrongly:

So we say:
1. we use .def files

but in that case Why do we still use the: #define MT4_EXPFUNC __declspec(dllexport)


http://msdn.microsoft.com/en-us/libr...=vs.80%29.aspx

Microsoft introduced __export in the 16-bit compiler version of Visual C++ to allow the compiler to generate the export names automatically and place them in a .lib file. This .lib file can then be used just like a static .lib to link with a DLL.
In newer compiler versions, you can export data, functions, classes, or class member functions from a DLL using the __declspec(dllexport) keyword. __declspec(dllexport) adds the export directive to the object file so you do not need to use a .def file.

Would that not mean: if I use a - def file there is not much point in using
#define MT4_EXPFUNC __declspec(dllexport)


My question rephrased would be:
Are there other good reason for using '#define MT4_EXPFUNC __declspec(dllexport) ' even though one has a .def file?
__Thanks__ MJ
  • #5
  • Sep 21, 2011 4:34am Sep 21, 2011 4:34am
Maybe you should ask these kinds of questions on the support forums / mailinglists for the compiler you are using, there you will most likely find the C++ gurus who know this compiler inside out and can explain you every detail about how it works and what you can/could/should do (or not do) and the reasons/implications/advantages/disadvantages.

Unfortunately I cannot help you since I don't use Microsoft compilers (and not even using C++ at all).
  • #6
  • Sep 21, 2011 7:34am Sep 21, 2011 7:34am
this is just my opinion based on experiments:

1. by putting __declspec(dllexport) in front of function declaration OR using def file, you tell compiler to export that function. if you dont use def file nor __declspec(dllexport) keyword, your function will not be exported.

2. __declspec(dllexport) will export the function using decorated name like ?orig_function_name@@xxx, while def file will export the function using the original name

3. using def file will give you undecorated function name

if you use def file, imo there is no need to use __declspec(dllexport)
  • #7
  • Last Post: Sep 22, 2011 8:11am Sep 22, 2011 8:11am
Quoting sangmane
this is just my opinion based on experiments:
if you use def file, imo there is no need to use __declspec(dllexport)
I understood it in the same way:
I had only wondered why for e.g. the MT4 sample code used both.


Thanks.
__Thanks__ MJ
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