Hello World for Pinvoke and Native Calls - visual-c++

Question

I am trying to do a very basic hello world for Pinvoke and native calls.
I create a single solution with 2 projects (one for the dll and one for the universal windows app)
So I end up with a project heirachy like this
There is one method in my dll (file NativeCalls.cpp):
#include "pch.h"
#include "NativeCalls.h"
#include <stdio.h>
MYAPI void print_line(const char* str) {
printf("%s\n", str);
}
On the C# side of things I have my NativeCalls.cs file
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
namespace MSSurfaceHubMonitoring
{
public static class NativeCalls
{
[DllImport("NativeCalls.dll")]
private static extern void print_line(string str);
public static void sayHelo()
{
print_line("Hello, PInvoke!");
}
}
}
At this point I will build and run it but get an error that it cannot find the dll
However I believe it to be the dependency and not the dll it self. I have changed the output directory of the dll to be in the root of where the UW app runs from (\bin\x86) so it really should be finding it. So like I said I think its the dependencies and not the actual dll.
Here is what I see in Dependency Walker
But I have installed all c++ packages I can get my hands on so I dont understand how to get the missing dependencies. Plus this is just a hello world, why do I need all these libraries.
FYI
My dll project is NOT referenced by the UW app. Im not sure thats needed or not? I dont think so though since this a runtime thing, so as long as the dll is there it should find it and read it. But regardless if I do try to add the project as a reference I get this error:

Answer 1

The biggest help to me was finding these method declarations (not even in the class)
extern "C" {
__declspec(dllexport) int getPageSize()
{
SYSTEM_INFO siSysInfo;
GetSystemInfo(&siSysInfo);
return siSysInfo.dwPageSize;
}
}
extern "C" {
__declspec(dllexport) Windows::Foundation::Collections::IMap<Platform::String^, int> ^getSystemInfo()
{
SYSTEM_INFO siSysInfo;
GetSystemInfo(&siSysInfo);
IMap<String^, int> ^ret =
ref new Platform::Collections::Map<String^, int>;
ret->Insert("oemId", siSysInfo.dwOemId);
ret->Insert("cpuCount", siSysInfo.dwNumberOfProcessors);
ret->Insert("pageSize", siSysInfo.dwPageSize);
ret->Insert("processorType", siSysInfo.dwProcessorType);
ret->Insert("maxApplicationAddress", siSysInfo.lpMinimumApplicationAddress);
ret->Insert("minApplicationAddress", siSysInfo.lpMaximumApplicationAddress);
ret->Insert("activeProcessorMask", siSysInfo.dwActiveProcessorMask);
return ret;
}
but in the end I was creating wrappers for things I didnt need to. in c# you can directly call the native methods without the need for a seperate dll or component project.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
namespace Monitoring
{
public static class NativeCallsWrapper
{
private static SYSTEM_INFO sysInfo = new SYSTEM_INFO();
private static MEMORYSTATUSEX mem = new MEMORYSTATUSEX();
[DllImport("kernel32.dll", SetLastError = false)]
public static extern void GetSystemInfo([In, Out] SYSTEM_INFO Info);
[return: MarshalAs(UnmanagedType.Bool)]
[DllImport("kernel32.dll", SetLastError = true)]
static extern bool GlobalMemoryStatusEx([In, Out] MEMORYSTATUSEX lpBuffer);
static NativeCallsWrapper()
{
GetSystemInfo(sysInfo);
GlobalMemoryStatusEx(mem);
}
[StructLayout(LayoutKind.Explicit)]
public struct SYSTEM_INFO_UNION
{
[FieldOffset(0)]
public UInt32 OemId;
[FieldOffset(0)]
public UInt16 ProcessorArchitecture;
[FieldOffset(2)]
public UInt16 Reserved;
}
public struct SYSTEM_INFO
{
public SYSTEM_INFO_UNION CpuInfo;
public UInt32 PageSize;
public UInt32 MinimumApplicationAddress;
public UInt32 MaximumApplicationAddress;
public UInt32 ActiveProcessorMask;
public UInt32 NumberOfProcessors;
public UInt32 ProcessorType;
public UInt32 AllocationGranularity;
public UInt16 ProcessorLevel;
public UInt16 ProcessorRevision;
}
[StructLayout(LayoutKind.Sequential)]
public class MEMORYSTATUSEX
{
public uint dwLength;
public uint dwMemoryLoad;
public ulong ullTotalPhys;
public ulong ullAvailPhys;
public ulong ullTotalPageFile;
public ulong ullAvailPageFile;
public ulong ullTotalVirtual;
public ulong ullAvailVirtual;
public ulong ullAvailExtendedVirtual;
public MEMORYSTATUSEX()
{
this.dwLength = (uint)Marshal.SizeOf(typeof(MEMORYSTATUSEX));
}
}
public static GeneralStatistics getGeneralStatistics()
{
GeneralStatistics generalStatistics = new GeneralStatistics();
generalStatistics.numberOfProcesses = (int)sysInfo.NumberOfProcessors;
generalStatistics.memoryTotal = mem.ullTotalPhys / 1048;
generalStatistics.memoryInUse = (mem.ullTotalPhys - mem.ullAvailPhys) / 1048;
return generalStatistics;
}
}
}