Calling a C++ function from C# program

I run into an issue calling a c++ function from a c# program. It works fine until I add the line "pcl::io::savePCDFileASCII("test_pcd.pcd", cloud);". Then I get the error:

Exception thrown: 'System.DllNotFoundException' in MIxed_Mode_Calling_App.exe
An unhandled exception of type 'System.DllNotFoundException' occurred in MIxed_Mode_Calling_App.exe
Unable to load DLL 'C:\Users\d\Box\Daniel\RE\Surface Project\PCL_Project\MixedMode\build\Debug\MixedMode.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)

The location is correct and the MixedMode.dll can be found at that location.

Why is the above named line causing issues in the dll but works fine in a simple .cpp program?

Thanks!

c++ function "MixedMode.h":

#ifndef MIXED_MODE_MULTIPLY_HPP
#define MIXED_MODE_MULTIPLY_HPP

#include <iostream>
#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>

extern "C"
{

    __declspec(dllexport) int __stdcall mixed_mode_multiply(int a, int b) {
        pcl::PointCloud<pcl::PointXYZ> cloud;

        // Fill in the cloud data
        cloud.width = 5;
        cloud.height = 1;
        cloud.is_dense = false;
        cloud.points.resize(cloud.width * cloud.height);

        for (auto& point : cloud)
        {
            point.x = 1024 * rand() / (RAND_MAX + 1.0f);
            point.y = 1024 * rand() / (RAND_MAX + 1.0f);
            point.z = 1024 * rand() / (RAND_MAX + 1.0f);
        }

        pcl::io::savePCDFileASCII("test_pcd.pcd", cloud); //If this line is removed it works.
        std::cerr << "Saved " << cloud.size() << " data points to test_pcd.pcd." << std::endl;

        for (const auto& point : cloud)
            std::cerr << "    " << point.x << " " << point.y << " " << point.z << std::endl;

        return (0);
    }
}
#endif

C++ "MixedMode.cpp":

#include "MixedMode.h"

c# program "Program.cs":

using System;
using System.Runtime.InteropServices;

namespace Mixed_Mode_Calling_App
{
    public class Program
    {
        [DllImport(@"C:\Users\d\Box\Daniel\RE\Surface Project\PCL_Project\MixedMode\build\Debug\MixedMode.dll", EntryPoint =
        "mixed_mode_multiply", CallingConvention = CallingConvention.StdCall)]
        public static extern int Multiply(int x, int y);
        public static void Main(string[] args)
        {
            int result = Multiply(7, 7);
            Console.WriteLine("The answer is {0}", result);
            Console.ReadKey();
        }
    }
}

As part of the troubleshooting, I created this .cpp program which runs fine.

#include <iostream>
#include <pcl/io/pcd_io.h>
#include <pcl/point_types.h>

int
main()
{
    pcl::PointCloud<pcl::PointXYZ> cloud;

    // Fill in the cloud data
    cloud.width = 5;
    cloud.height = 1;
    cloud.is_dense = false;
    cloud.points.resize(cloud.width * cloud.height);

    for (auto& point : cloud)
    {
        point.x = 1024 * rand() / (RAND_MAX + 1.0f);
        point.y = 1024 * rand() / (RAND_MAX + 1.0f);
        point.z = 1024 * rand() / (RAND_MAX + 1.0f);
    }

    pcl::io::savePCDFileASCII("test_pcd.pcd", cloud);
    std::cerr << "Saved " << cloud.size() << " data points to test_pcd.pcd." << std::endl;

    for (const auto& point : cloud)
        std::cerr << "    " << point.x << " " << point.y << " " << point.z << std::endl;

    return (0);
}