C++ how to tell if static .lib is valid, callable from external code

StackOverflow https://stackoverflow.com/questions/21690466

  •  09-10-2022
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Question

I've got a C++ .lib file provided by a vendor, with some sparse documentation and sample code. My task is to use it to build a prototype to showcase the vendor's technology.

Being a (mostly) C#/Java developer, I'm trying to hack together something basic using this lib and using the tricks I know - all of which are leading me to believe I'm missing something (or the lib is...)

dumpbin /exports foo.bin doesn't show any exported functions:

E:\SDKs\Acme\lib>dumpbin /exports foo.lib
Microsoft (R) COFF/PE Dumper Version 10.00.40219.01
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file foo.lib

File Type: LIBRARY

  Summary

   1AB29A0 .bss
      6BD0 .data
      AAE0 .nocopy
    C5A0E0 .noinit
    1954D0 .rdata
     19000 .scratch
     C1CA0 .text
    492000 .vram

lib /list foo.lib shows a number what I assume are function names with a .w32o extension. Based on the function names, and the type of business the vendor is in, these all look valid.

The vendor's README says to initiate the library by calling its __foo_entry() function. Dumpbin /SYMBOLS does in fact show this function:

040 00002826 SECT1  notype ()    External     | __foo_entry

The vendor's sample code loads the library (using dlopen, which is a *nix way of loading a library according to my understanding.)

But I've created a VS2010 project, and have tried to load the library like so:

System::Void load(){

    HINSTANCE sdl_library = LoadLibrary(TEXT("E:\\SDKs\\Acme\\lib\\foo.lib"));

    if (sdl_library == NULL) {
        Console::WriteLine("error");
    } else {
        Console::WriteLine("success");
    }
 }

When the project tries to the line containing "LoadLibrary", the debugger throws a Bad Image exception: "E:\SDKs\Acme\lib\foo.lib" is either not designed to run on Windows or it contains an error..."

Dependency walker is not much help here because the .lib is static.

So: is it a valid .lib or not?

The visual studio command line tools seem to indicate it is valid, but trying to load it into a project indicates it's not.

Was it helpful?

Solution

On Windows, shared libraries and LoadLibrary are associated with the file extension .dll.

.lib suggests that you should try static linking, like a linux .a file. .lib files may contain actual code, but are also used for an import library, such that static linking will generate a binary that requires a DLL at runtime.

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