Error when trying to load DLL with QLibrary
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I'm using Qt5 and I want to work with a DLL file that I know is fully functional and which I can even use with other programs on my computer with no problems.
However, when I try to load it in my program using QLibrary, I get an error message.
Here's the .cpp file:
#include <QLibrary> #include <QDebug> myObject::myObject() { QLibrary myLibrary("./myDll"); myLibrary.load(); if(myLibrary.isLoaded()) qDebug() << "It worked!"; else { qDebug() << myLibrary.errorString(); } }When I run this code, I get this error message:
"Cannot load library .\myDll: Unknown error 0x000000c1."
I've run Dependency Walker and I get a lot of yellow flags. However, I can't understand how I've been using this DLL with other (3rd party) programs on the same computer without any problems.
I contacted the developer of the DLL and he told me this library is a plain C (not C++) 32-bit library, and that perhaps I should adjust some of the compiler options. If this is the case, which options should I change?
@Linhares said in Error when trying to load DLL with QLibrary:
QLibrary myLibrary("./myDll");
You are using a relative path: are you sure the lib is in the current working directory?
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I'm using Qt5 and I want to work with a DLL file that I know is fully functional and which I can even use with other programs on my computer with no problems.
However, when I try to load it in my program using QLibrary, I get an error message.
Here's the .cpp file:
#include <QLibrary> #include <QDebug> myObject::myObject() { QLibrary myLibrary("./myDll"); myLibrary.load(); if(myLibrary.isLoaded()) qDebug() << "It worked!"; else { qDebug() << myLibrary.errorString(); } }When I run this code, I get this error message:
"Cannot load library .\myDll: Unknown error 0x000000c1."
I've run Dependency Walker and I get a lot of yellow flags. However, I can't understand how I've been using this DLL with other (3rd party) programs on the same computer without any problems.
I contacted the developer of the DLL and he told me this library is a plain C (not C++) 32-bit library, and that perhaps I should adjust some of the compiler options. If this is the case, which options should I change?
@Linhares said in Error when trying to load DLL with QLibrary:
"Cannot load library .\myDll: Unknown error 0x000000c1."
(Additional to @jsulm.) Most (in fact I think it is mandatory?) Windows DLL files end in
.DLL... ?EDIT
Given the errorCannot load library .\myDll: Unknown error 0x000000c1that might it is found, somehow, but is "not acceptable". Googledll Unknown error 0x000000c1, seems to only come from Qt programs, e.g. see Cannot load library *.dll Unknown error 0x000000c1The error list you need is here. The symbolic name for that error is ERROR_BAD_EXE_FORMAT, and the error message is <filesoandso> is not a valid Win32 application. The DLL you're trying to open is either corrupt, or - most likely - it is for a different architecture. If you're compiling for 32 bits, use 32-bit DLLs. If you're compiling for 64 bits, use 64-bit DLLs.
If the developer says it is 32-bit are you compiling your Qt program 32-bit or 64-bit? :)
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@Linhares said in Error when trying to load DLL with QLibrary:
QLibrary myLibrary("./myDll");
You are using a relative path: are you sure the lib is in the current working directory?
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@jsulm Yes, the lib is in the folder. From the error message, I understand the program can find the lib, but it can't load it correctly.
@Linhares Take a look at this: https://stackoverflow.com/questions/61080829/cannot-load-library-dll-unknown-error-0x000000c1
Is it possible that this DLL is built for a different architecture? Like your app is x86_64, but the lib x86. -
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@Linhares
Although you have said "Yes, the lib is in the folder", and presumably you claim the relative path./myDllfinds it successfully, you still have not said anything about myMost (in fact I think it is mandatory?) Windows DLL files end in
.DLL... ?? [Oh, are we supposed to guess that you are in fact not using literal
./myDllbut rather./something.dll??] You could always do aQFileInfoon whatever you pass to make sure....Otherwise @mchinand's suggestion of quickly making your application actually try to link with
thedll.lib(you do have that?) by calling a function in it from your Qt program is a good idea to get a better error message, -
It turned out that I noticed I was being fooled by Qt Creator. Although the settings showed MSVC 32-bit as default, it was not installed. Hence, I was running a 64-bit compiler and thinking I was using a 32-bit one.
Thank you guys for the help with this! -
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