Visual C++ : XGBoost does not work when called from a DLL - c++

Question

I have a requirement to use XGBoost within a Visual C++ project DLL.
I have been able to download and build the XGBoost source using VC++ and CMake.
When I include the XGBoost code in a test console application, it works fine.
However, when I try to replicate what I've done with the console application in a DLL project, it won't compile.
I am struggling to even use a basic XGBoost type within the project.
I suspect the problem is my ignorance with DLL projects and would appreciate your help.
Here's what's happening in my DLL project:
When I use the following include as the very first line in a cpp class file, it compiles:
#include <xgboost\c_api.h>
With it compiling, if I try to use a simple type defined in this include file, the build fails with the following message:
...\dll_test\xgb_driver.cpp(20): error C2065: 'BoosterHandle': undeclared identifier
This is the line that causes the error:
BoosterHandle my_handle;
"BoosterHandle" is in fact defined in <xgboost\c_api.h>
When I put the include below any other include, I get the following error messages:
1>c:\tools\src\xgboost\include\xgboost\c_api.h(29): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\tools\src\xgboost\include\xgboost\c_api.h(29): error C2146: syntax error: missing ';' before identifier 'bst_ulong'
Below is a little more information on what I did to get XGBoost working with a console app and how I created the DLL project.
=-=-=-=-=-=
Here's what I did to use XGBoost with a console. Everything about it seems to work. I've tested the model predictions, and they are
consistent with what I'm seeing in R.
Using the documentation found here:
https://xgboost.readthedocs.io/en/latest/build.html
I downloaded the XGBoost source and built it using CMake and Visual Studio 2015.
Under Project > Linker > Input > Additional Dependencies,
I added the xgboost.lib file
Under Project > Linker > General > Additional Library Directories
I added a reference to ...\xgboost\build\Release
Under Project > VC++ Directories > Include Directories
I added the path to ...\xgboost\rabit\include and ...\xgboost\include
I put the xgboost.dll in the directory where the .exe is generated.
From here, it was smooth sailing.
=-=-=-=-=-=
Here's what I've done to create a Visual C++ DLL Project:
After choosing File > New > Project, I select an ATL DLL Project (this is part of the project requirement).
For the XGBoost include to the project, I repeated steps 1-5 above, but placed the xgboost.dll file where the
project DLL would be generated.
Here is the source for the header file for the simple class I have created:
#pragma once
class XGB_Driver
{
public:
XGB_Driver();
~XGB_Driver();
float callXGB(float sample_input);
};
Here is the source for the simple cpp file:
#include <xgboost/c_api.h>
#include "stdafx.h"
#include "XGB_Driver.h"
XGB_Driver::XGB_Driver()
{
}
XGB_Driver::~XGB_Driver()
{
}
float XGB_Driver::callXGB(float simple_input) {
BoosterHandle my_handle;
return(0);
}
Why this doesn't work for the ATL DLL project, but does for the console app really has me banging my head against the keyboard.
Your help would be very much appreciated.
Best,
Dave

Answer 1

With the help of CristiFati, I believe this question has been answered.
For whatever reason, it seems that using XGBoost with C++ in a DLL project requires additional includes above and beyond what is required for using it in a console application.
I am currently building the DLL project with the addition of:
#include <cstdint>