I am modifying some old VB6 code and there are a number of calls to a subroutine called SDKPress(Index as integer, PressStatus as Integer, PressX as double, PressY as double, PressDataX as double, PressDataY as double).
(This routine returns the position of the mouse click and Index returns which graph on a form the mouse is in.)
Since there is no code for this in the project, I assume it is from some Windows software development kit. However, there is no trace of it on the development PC. just an SDK directory in the VisualBasic directory containing winsdk_web.exe.
I cannot call that subroutine from another project. Where does the subroutine live? Where can I find documentation on it? How can I get it in a form where I can use it on another project?
To find out where it lives. Put the cursor in one of the routine calls in the IDE, right-click on it, and choose go to definition. See where it takes you.
It may be an ordinary routine in a code file in your project.
It may be a routine in a DLL which is imported into your project via a Declare statement.
It may be a routine in a COM/ActiveX DLL or OCX control or even ActiveX EXE. In which case the IDE will show you the "object browser" window and you should be able to figure out where the routine lives, and go from there. I.e. figure out how to add a reference to it into another VB project, and how to install/register the relevant DLL/OCX/EXE on another PC.
OR, and I'm sure you tried this already, but just in case, search the source code for the routine name. Use Ctr-F or menu item Edit-Find in the VB IDE.
DLL files contains the API functions, vb6 code will load the DLL (Declare Function SDKPress Lib "DLLName" ....) and call the functions, use a tool like DllExpView: https://www.nirsoft.net/utils/dll_export_viewer.html and list DLLs and their functions. Or it also might be an internal subroutine/function.
If the original program which uses the SDK runs, you can gather some information using Process Monitor and Process Explorer. These can help you locate dependencies of many types.
I'd start with the second - when you run your program, ProcExp will show you all the files, including DLLs, that are loaded into the process. This alone might give you some insight.
If that is insufficient then use ProcMon to actively monitor the activities of your program. While ProcExp is basically a snapshot in time, ProcMon will dynamically record many of the actions of your program, including how it searches for and ultimately loads DLLs.
https://learn.microsoft.com/en-us/sysinternals/downloads/procmon
https://learn.microsoft.com/en-us/sysinternals/downloads/process-explorer
I have found these tools to be invaluable on many occasions. They help to break down the "black box" around a running process which appears in many programmers minds.
I want to hook into a DLL library and manipulate the arguments passed into it and manipulate its behavior. I don't want to have to maintain a separate fork by rebuilding the library and tracking changes. Instead, I want to use my library as a way to just pass calls on to the target library.
I can see what functions are exposed in the DLL but I only need to implement a subset of these. Is there a way to use a debugger to monitor and get a list of functions being called?
What you want to make a is a proxy DLL. You replace the original DLL with yours and rename the original, then you LoadLibrary() the original renamed DLL. For functions you don't want to log or modify, you just pass through to the real DLL function. Otherwise you modify the arguments and then pass it through.
There are many tools which can help you generate a proxy DLL
https://github.com/maluramichael/dll-proxy-generator
https://github.com/zeroKilo/ProxyDllMaker
https://github.com/kevinalmansa/DLL_Wrapper
I am beginer in windows programming, and trying to understand use of DLL and lib in an existing project implementation. From my understanding LIB and dll are used to reuse the validated code and reduce the size of exe, by loading them on need basis. Although there are quite a few articles on internet explained about this, but I am looking for any example with diagram(How is the flow from Application programme to Lib/dll and vice versa). I am getting lots of error related to inappropriate setting of lib in resource and C/C++ configuration in my project, but due to my limited understanding of the calling between app-lib-dll i am unable to fix them.
Looking forward for some quick refrence documents/links/video to understand these concepts.
Lib files and DLL files provide ways to include code in your process. For a lib file this inclusion is done by the linker to add code to your exe. For a DLL file the inclusion is done by the operating system when your exe is loaded into memory - before the program starts. So by the time your program starts all the code is in your process memory and calling a lib function or calling a DLL function is done the same way, or almost the same way, that calls to your own functions are done. So the "flow" that you are asking about is not significantly different for a lib or DLL. A call is a call, no matter how the called function got into memory.
Maybe that's silly, but I'm confused again when trying to find appropriate names for my projects.
I have a solution with two projects. First project is a library, which will be used by other libraries in the future, for creating plugins for my app. Second project is a exe, which uses first project to create GUI and do some stuff, eg. load plugins.
In similar situation, when one project is a dll and second is an exe, how do you choose names for each project?
Lets say, that I would like to peek a name GraphDemonstration. The exe should be GraphDemonstrationGUI and dll - GraphDemonstration? But exe is not just a GUI. So maybe GraphDemonstration for exe and GraphDemonstrationLib for dll?
I have had similar situation in the past. Maybe there is some kind of naming convention? I don't even know if my "problem" is related to VS only.
GraphDemonstration for your EXE is fine because it describes the purpose of the EXE. However, you said the library will be used by other projects later so the "GraphDemonstration" part of GraphDemonstrationLibrary may not be the best choice. Perhaps GraphLibrary, or GraphHelper, or maybe more specific depending on what is actually included in the library. For example, if the library handles instantiating an Excel object to generate a graph you could call it ExcelGraphHelper.dll.
If this is library of main class CSomeClass I name project SomeClassLibrary.
For projects smillary but non from main object.
I want to know the exact difference between the dll and exe file.
I don't know why everybody is answering this question in context of .NET. The question was a general one and didn't mention .NET anywhere.
Well, the major differences are:
EXE
An exe always runs in its own address space i.e., It is a separate process.
The purpose of an EXE is to launch a separate application of its own.
DLL
A dll always needs a host exe to run. i.e., it can never run in its own address space.
The purpose of a DLL is to have a collection of methods/classes which can be re-used from some other application.
DLL is Microsoft's implementation of a shared library.
The file format of DLL and exe is essentially the same. Windows recognizes the difference between DLL and EXE through PE Header in the file. For details of PE Header, You can have a look at this Article on MSDN
EXE:
It's a executable file
When loading an executable, no export is called, but only the module entry point.
When a system launches new executable, a new process is created
The entry thread is called in context of main thread of that process.
DLL:
It's a Dynamic Link Library
There are multiple exported symbols.
The system loads a DLL into the context of an existing process.
For More Details: http://www.c-sharpcorner.com/Interviews/Answer/Answers.aspxQuestionId=1431&MajorCategoryId=1&MinorCategoryId=1
http://wiki.answers.com/Q/What_is_the_difference_between_an_EXE_and_a_DLL
Reference: http://www.dotnetspider.com/forum/34260-What-difference-between-dll-exe.aspx
The difference is that an EXE has an entry point, a "main" method that will run on execution.
The code within a DLL needs to be called from another application.
There are a few more differences regarding the structure you could mention.
Both DLL and EXE share the same file structure - Portable Executable, or PE. To differentiate between the two, one can look in the Characteristics member of IMAGE_FILE_HEADER inside IMAGE_NT_HEADERS. For a DLL, it has the IMAGE_FILE_DLL (0x2000) flag turned on. For a EXE it's the IMAGE_FILE_EXECUTABLE_IMAGE (0x2) flag.
PE files consist of some headers and a number of sections. There's usually a section for code, a section for data, a section listing imported functions and a section for resources. Some sections may contain more than one thing. The header also describes a list of data directories that are located in the sections. Those data directories are what enables Windows to find what it needs in the PE. But one type of data directory that an EXE will never have (unless you're building a frankenstein EXE) is the export directory. This is where DLL files have a list of functions they export and can be used by other EXE or DLL files. On the other side, each DLL and EXE has an import directory where it lists the functions and DLL files it requires to run.
Also in the PE headers (IMAGE_OPTIONAL_HEADER) is the ImageBase member. It specifies the virtual address at which the PE assumes it will be loaded. If it is loaded at another address, some pointers could point to the wrong memory. As EXE files are amongst the first to be loaded into their new address space, the Windows loader can assure a constant load address and that's usually 0x00400000. That luxury doesn't exist for a DLL. Two DLL files loaded into the same process can request the same address. This is why a DLL has another data directory called Base Relocation Directory that usually resides in its own section - .reloc. This directory contains a list of places in the DLL that need to be rebased/patched so they'll point to the right memory. Most EXE files don't have this directory, but some old compilers do generate them.
You can read more on this topic # MSDN.
This answer was a little more detailed than I thought but read it through.
DLL:
In most cases, a DLL file is a library. There are a couple of types of libraries, dynamic and static - read about the difference. DLL stands for dynamic link library which tells us that it's a part of the program but not the whole thing. It's made of reusable software components (library) which you could use for more than a single program. Bear in mind that it's always possible to use the library source code in many applications using copy-paste, but the idea of a DLL/Static Library is that you could update the code of a library and at the same time update all the applications using it - without compiling.
For example:
Imagine you're creating a Windows GUI component like a Button. In most cases you'd want to re-use the code you've written because it's a complex but a common component - You want many applications to use it but you don't want to give them the source code You can't copy-paste the code for the button in every program, so you decide you want to create a DL-Library (DLL).
This "button" library is required by EXEcutables to run, and without it they will not run because they don't know how to create the button, only how to talk to it.
Likewise, a DLL cannot be executed - run, because it's only a part of the program but doesn't have the information required to create a "process".
EXE:
An executable is the program. It knows how to create a process and how to talk to the DLL. It needs the DLL to create a button, and without it the application doesn't run - ERROR.
hope this helps....
Both DLL and EXE are Portable Executable(PE) Formats
A Dynamic-link library (DLL) is a library and therefore can not be executed directly. If you try to run it you will get an error about a missing entry point. It needs an entry point (main function) to get executed, that entry point can be any application or exe. DLL binding occurs at run-time. That is why its called "Dynamic Link" library.
An Executable (EXE) is a program that can be executed. It has its own entry point. A flag inside the PE header indicates which type of file it is (irrelevant of file extension). The PE header has a field where the entry point for the program resides. In DLLs it isn't used (or at least not as an entry point).
There are many software available to check header information. The only difference causing both to work differently is the bit in header as shown in below diagram.
EXE file has only single main entry means it is isolated application, when a system launches exe, a new process is created while DLLs have many entry points so when application use it no new process started, DLL can be reused and versioned. DLL reduces storage space as different programs can use the same dll.
Dll v/s Exe
1)DLL file is a dynamic link library which can be used in exe files and
other dll files.
EXE file is a executable file which runs in a separate
process which is managed by OS.
2)DLLs are not directly executable . They are separate files containing functions that can be called by programs and other DLLs to perform computations and functions.
An EXE is a program that can be executed . Ex :Windows program
3)Reusability
DLL: They can be reused for some other application. As long as the coder knows the names and parameters of the functions and procedures in the DLL file .
EXE: Only for specific purpose .
4)A DLL would share the same process and memory space of the calling application while an
EXE creates its separate process and memory space.
5)Uses
DLL: You want many applications to use it but you don't want to give them the source code You can't copy-paste the code for the button in every program, so you decide you want to create a DL-Library (DLL).
EXE: When we work with project templates like Windows Forms Applications, Console Applications, WPF Applications and Windows Services they generate an exe assembly when compiled.
6)Similarities :
Both DLL and EXE are binary files have a complex nested structure defined by the Portable Executable format, and they are not intended to be editable by users.
Two things: the extension and the header flag stored in the file.
Both files are PE files. Both contain the exact same layout. A DLL is a library and therefore can not be executed. If you try to run it you'll get an error about a missing entry point. An EXE is a program that can be executed. It has an entry point. A flag inside the PE header indicates which file type it is (irrelevant of file extension). The PE header has a field where the entry point for the program resides. In DLLs it isn't used (or at least not as an entry point).
One minor difference is that in most cases DLLs have an export section where symbols are exported. EXEs should never have an export section since they aren't libraries but nothing prevents that from happening. The Win32 loader doesn't care either way.
Other than that they are identical. So, in summary, EXEs are executable programs while DLLs are libraries loaded into a process and contain some sort of useful functionality like security, database access or something.
The .exe is the program. The .dll is a library that a .exe (or another .dll) may call into.
What sakthivignesh says can be true in that one .exe can use another as if it were a library, and this is done (for example) with some COM components. In this case, the "slave" .exe is a separate program (strictly speaking, a separate process - perhaps running on a separate machine), but one that accepts and handles requests from other programs/components/whatever.
However, if you just pick a random .exe and .dll from a folder in your Program Files, odds are that COM isn't relevant - they are just a program and its dynamically-linked libraries.
Using Win32 APIs, a program can load and use a DLL using the LoadLibrary and GetProcAddress API functions, IIRC. There were similar functions in Win16.
COM is in many ways an evolution of the DLL idea, originally concieved as the basis for OLE2, whereas .NET is the descendant of COM. DLLs have been around since Windows 1, IIRC. They were originally a way of sharing binary code (particularly system APIs) between multiple running programs in order to minimise memory use.
An EXE is visible to the system as a regular Win32 executable. Its entry
point refers to a small loader which initializes the .NET runtime and tells
it to load and execute the assembly contained in the EXE.
A DLL is visible to the system as a Win32 DLL but most likely without any
entry points. The .NET runtime stores information about the contained
assembly in its own header.
dll is a collection of reusable
functions where as an .exe is an
executable which may call these
functions
An exe is an executible program whereas A DLL is a file that can be loaded and executed by programs dynamically.
● .exe and dll are the compiled version of c# code which are also called as
assemblies.
● .exe is a stand alone executable file, which means it can executed directly.
● .dll is a reusable component which cannot be executed directly and it requires
other programs to execute it.
For those looking a concise answer,
If an assembly is compiled as a class library and provides types for other assemblies to use, then it has the ifle extension .dll (dynamic link library), and it cannot be executed standalone.
Likewise, if an assembly is compiled as an application, then it has the file extension .exe (executable) and can be executed standalone. Before .NET Core 3.0, console apps were compiled to .dll fles and had to be executed by the dotnet run command or a host executable. - Source
Difference in DLL and EXE:
1) DLL is an In-Process Component which means running in the same memory space as the client process. EXE is an Out-Process Component which means it runs in its own separate memory space.
2) The DLL contains functions and procedures that other programs can use (promotes reuability) while EXE cannot be shared with other programs.
3) DLL cannot be directly executed as they're designed to be loaded and run by other programs. EXE is a program that is executed directly.
The major exact difference between DLL and EXE that DLL hasn't got an entry point and EXE does. If you are familiar with c++ you can see that build EXE has main() entry function and DLL doesn't :)