DLL Load Library - Error Code 126

Question

I'm using the 'LoadLibrary' from the Windows API, when I run the application, it throws me an error code 126. I read that it may be caused by dependencies, I checked what's wrong with some applications like Dependency Walker, but everything was fine.

LoadLibrary in the application:

            HMODULE dll_mod = LoadLibrary(L"path_to_dll");
            if(dll_mod==NULL){
                std::stringstream error;
                error << "Could not load plugin located at:\n" << file_full.toStdString() << "\n" << "Error Code: " << GetLastError();
                FreeLibrary(dll_mod);
                return error.str();
            }

Plugin code:

#include "stdafx.h"
#define DLL_EXPORT
#define PLUGIN_STREAM __declspec(dllexport)
#include <iostream>
#include <vector>
using std::vector;
using std::string;
// Init event (After the loading)
extern "C"{
PLUGIN_STREAM int onInit(char* argv){
return 0;
}
PLUGIN_STREAM void pluginInfo(vector<string> & info){
info.push_back("media_event=false");
    info.push_back("status_event=false");
    info.push_back("send_event=true");
    info.push_back("plugin_name='RadioStream'");
    info.push_back("description='This plugin was designed for that people that wants to listen to radio music.\nYou can register your radio and play it later, also we have a gallery of radios that you can check.\nThis plugin is original of Volt and it's originally implemented in the application.'");
    info.push_back("success:0");
    info.push_back("error:1=Could not open data file");
    info.push_back("error:2=Could not prepare plugin");
    info.push_back("alert:40=Could not connect to that radio");
}
}

Answer 1

Windows dll error 126 can have many root causes. The most useful methods I have found to debug this are:

1. Use dependency walker to look for any obvious problems (which you have already done)
2. Use the sysinternals utility Process Monitor https://learn.microsoft.com/en-us/sysinternals/downloads/procmon from Microsoft to trace all file access while your dll is trying to load. With this utility, you will see everything that that dll is trying to pull in and usually the problem can be determined from there.

Answer 2

This can also happen when you're trying to load a DLL and that in turn needs another DLL which cannot be not found.

Answer 3

This error can happen because some MFC library (eg. mfc120.dll) from which the DLL is dependent is missing in windows/system32 folder.

Answer 4

In my case it was all about character sets v.s. form of loader function. This is visual studio 2019 setting at Project/Properties/Configuration Properties/Advanced/Character Set which has two choices:

1.Use Multi-Byte Character Set ->call it mb

2.Use Unicode Character Set -> call it uc

 My test revealed:

      const char*  fileName =  ".\\Debug\\Win32\\Dll1.dll";
    
         void* module = LoadLibrary((LPCWSTR)fileName); 
         //compiles no mb, compiles uc, uc run fails with 126
          
         void* module = LoadLibrary((LPCSTR)fileName); 
         //compiles mb,runs mb, no uc
          
         void* module = LoadLibraryA(fileName); //note explicit A
         //compiles mb,runs mb, compiles uc,runs uc
    
     DWORD lasterror = GetLastError();//0 is ok

Today I banged my head again to 126. I learned one thing that makes 126 happen again on top of those previous examples is chained loading of java's virtual machine dll from my_dll. In my case my_dll needs to have jvm.dll marked as "delay loaded". Setting is at project level: Configuration Properties/Linker/Input/Delay Loaded Dlls where I wrote jvm.dll; This error is something I can repeat.

Answer 5

In my case, the name of the dll inside LoadLibrary(..) was incorrect.

Answer 6

Changing project's property 'Configuration Properties'/'С/С++'/'Code Generation'/'Runtime Library' from Multi-Threaded DLL(/MD) to Multi-Threaded(/MT) helped me in the same case.

Answer 7

This worked for me Visual C++ Redistributable Packages