R – How to use the .def file for explicit linking

dllfunctionlinkervisual-studio-2005

I am facing the the problem to link to a third party dll. It is windows mobile application, where I am try to link to this third party dll.

Here first I had the dll and lib file. I was not able to link to it explicitly, but implicit linking is working. In the explicit linking the getprocaddress was failing. The dumpbin showed only the dllmain functions being exposed and no other function being exposed, hence the getprocaddress was failing.
However my application doesnot start if the dll is not found/installed in the device. It is expected as it is imlicit linking of a dll hence my application does not start.

I reported this to the third party dll provider and said that I want the explicit linking as the dll takes more space in my application if it is linked implicitly.
They replied by providing the .def file and said that I can use this .def file in my app to explicitly link to a dll.

I don't know how to use this .def file to explicitly link to a dll. Can any one please explain briefly about how to use this .def file in my app to explicitly link to a dll.

Best Answer

Use the *.def file when you build the DLL, to specify what function names the DLL is supposed to export.

After the DLL is built, use dumpbin /exports to verify that the functions are indeed exported from the DLL.

After you have verified that the DLL is exporting functions, you can either link to them at run-time using LoadLibray/GetProcAddress, and/or you can link to them at build-time by passing the DLL's *.lib file (which was created when you built the DLL using its *.def file) as an argument to your application's linker.

Related Solutions

Visual-studio – How to set the path to a DLL file in Visual Studio

Go to project properties (Alt+F7)
Under Debugging, look to the right
There's an Environment field.
Add your relative path there (relative to vcproj folder) i.e. ..\some-framework\lib by appending PATH=%PATH%;$(ProjectDir)\some-framework\lib or prepending to the path PATH=C:\some-framework\lib;%PATH%
Hit F5 (debug) again and it should work.

Javascript – the use of the JavaScript ‘bind’ method

Bind creates a new function that will force the this inside the function to be the parameter passed to bind().

Here's an example that shows how to use bind to pass a member method around that has the correct this:

var myButton = {
  content: 'OK',
  click() {
    console.log(this.content + ' clicked');
  }
};

myButton.click();

var looseClick = myButton.click;
looseClick(); // not bound, 'this' is not myButton - it is the globalThis

var boundClick = myButton.click.bind(myButton);
boundClick(); // bound, 'this' is myButton

Which prints out:

OK clicked
undefined clicked
OK clicked

You can also add extra parameters after the 1st (this) parameter and bind will pass in those values to the original function. Any additional parameters you later pass to the bound function will be passed in after the bound parameters:

// Example showing binding some parameters
var sum = function(a, b) {
  return a + b;
};

var add5 = sum.bind(null, 5);
console.log(add5(10));

Which prints out:

Check out JavaScript Function bind for more info and interactive examples.

Update: ECMAScript 2015 adds support for => functions. => functions are more compact and do not change the this pointer from their defining scope, so you may not need to use bind() as often. For example, if you wanted a function on Button from the first example to hook up the click callback to a DOM event, the following are all valid ways of doing that:

var myButton = {
  ... // As above
  hookEvent(element) {
    // Use bind() to ensure 'this' is the 'this' inside click()
    element.addEventListener('click', this.click.bind(this));
  }
};

Or:

var myButton = {
  ... // As above
  hookEvent(element) {
    // Use a new variable for 'this' since 'this' inside the function
    // will not be the 'this' inside hookEvent()
    var me = this;
    element.addEventListener('click', function() { me.click() });
  }
};

Or:

var myButton = {
  ... // As above
  hookEvent(element) {
    // => functions do not change 'this', so you can use it directly
    element.addEventListener('click', () => this.click());
  }
};

Best Answer

Related Solutions

Visual-studio – How to set the path to a DLL file in Visual Studio

Javascript – the use of the JavaScript ‘bind’ method

Related Topic