How to identify the location of the dll and call dllimport?

I have a class that uses the DLLImport().
In the first parameter, you must pass the path + name of the dll.


 c:\\project \\bin\\[name of dll]

 When I run in the local environment, the process runs successfully.

 How to access it with web application?

 How to identify the application folder and pass the first parameter of DllImport?

 Something like ...

 _dllLocation const string = "c: \\ project \\ bin \ [dll name] ";

 [DllImport (_dllLocation, CharSet = CharSet.Ansi, CallingConvention CallingConvention.Cdecl =)]

 How to pass the first parameter without passing a fixed path?
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Waldir-PRGAuthor Commented:
a correction in the statement...

const string _dllLocation = "c:\\projeto\\Bin\\[nome da dll]";

From the context of a web application, you can get the current application path with this:


This is a virtual path (URL), and not a file system path. To convert it to a file system path, use this:


That gives you the absolute path to the current web application root folder. So, assuming the DLL you want to load is in the app's "bin" folder, this would be the path to your DLL:

HttpContext.Current.Request.MapPath(HttpContext.Current.Request.ApplicationPath) + "\\bin\\" + dllName
Todd GerbertIT ConsultantCommented:
I'm not entirely sure you can use a variable in the DllImport attribute, it might need to be hard coded path (I'm going off  memory though, and can't be positive without looking it up). Though if the DLL's in the system PATH or in your web app's Bin folder you should be able to specify just the file name.
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Waldir-PRGAuthor Commented:
Ok. I understood that I can use

HttpContext.Current.Request.MapPath(HttpContext.Current.Request.ApplicationPath) + "\\bin\\" + dllName

to identify the path.

However, DLLimport just receives in the first parameter a field "const string" and I can't save this call in a field "const" .

If a use this code:

const string _dllLocation = System.Web.HttpContext.Current.Request.MapPath(System.Web.HttpContext.Current.Request.ApplicationPath) + "\\bin\\nameofdll";

[DllImport(_dllLocation, ....

I generate a mistake:

The expression needs to be const.

Do you understant ?

How can I save or convert  "System.Web.HttpContext.Current.Request.MapPath...." to a "const string" ?
Todd GerbertIT ConsultantCommented:
Yes, that means you can't use a variable name in the DllImport, it needs to be a hard-coded string (as I suspected, above http:#a35356078).

// This doesn't work because you can't use a variable in DllImport
string dllLocation = @"C:\Folder\library.dll";

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// The library location needs to be given directly to the DllImport attribute

Open in new window

I assume this is a DLL you've created yourself, and not a part of Windows?

You should be able to put the DLL in your application's Bin folder and just specifying it's name in the DllImport attribute, or using a relative path, e.g.:

Open in new window

You can also put the DLL in the system path and use just it's name.

MSDN describes the values you can use:

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Waldir-PRGAuthor Commented:
I tried to use this command, starting the project in localhost, but a received an error when I called the function that uses DLLImport

It's not possible to load DLL 'bin\nameLibrary.dll' (Exception HRESULT: 0x8007007E)

I just got to call the dll when I specified the full path


Same putting @, the result was equals

the dll was loaded

Same putting two bars between the folders at the path, with a simple path
It was showed the error (Exception HRESULT: 0x8007007E)

I will try to save the dll inside the path system32..
Waldir-PRGAuthor Commented:
Perfect tgerbert!

I saved just the name of dll in the first parameter of DLLImport.

To load the project at the localhost, I needed do save the dll at the path

Windows\syswow64 (Windows 64 bits).

To load at the web, just the name of ddl it was sufficient.

Thanks a lot.
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