外部库错误 c++

我在编译DLL文件项目时遇到了一些问题。有 2 个文件 CDLL.h 和 CDLL.cpp：

CDLL.h：

#pragma once
namespace CDLL {
    class CDLL
    {
        static unsigned char TransLut[256];
    public:
        __declspec(dllexport) void build_lookup_table ( int contr);
        __declspec(dllexport) bool Contrast(HBITMAP * phBitmap, int iCount);
    };
}

CDLL.cpp：

#include "Stdafx.h"
#include "CDLL.h"
#include <math.h>
#include <windows.h>
namespace CDLL
{
    void CDLL::build_lookup_table(int contr)
    {
        float step, step_value;
        for (int i=0; i < 256; i++)
            TransLut[i] = i;
        if (contr > 0)
        {
            unsigned int MinBin = contr;
            unsigned int MaxBin = 255 - contr;
            step = sqrt((double)contr)/contr;
            step_value = 0.0;
            for (int i = 0; i < MinBin; i++)
            {
                TransLut[i] = (unsigned char)step_value;
                step_value += step;
            }
            step = 256.0f / (float)(MaxBin-MinBin);
            for (int i = MinBin; i <= MaxBin; i++)
            {
                if (step_value > 255.0f)
                {
                    step_value = 255.0f;
                    step = 0.0f;
                }
                TransLut[i] = (unsigned char)step_value;
                step_value += step;
            }
            for (int i = MaxBin + 1; i < 256; i++)
                TransLut[i] = 255;
        }
        else if (contr < 0)
        {
                step = (256.0+(float)(contr*2))/256.0;
                step_value = (float)contr * -1.0;
                for (int i = 0;i < 256; i++)
                {
                    TransLut[i] = (unsigned char)step_value;
                    step_value += step;
                }
        }
    }
    bool CDLL::Contrast(HBITMAP * phBitmap, int iCount) 
    {
        BITMAP bm;
        BYTE * pBits;
        RGBQUAD * pRgb;
        WORD wByteCount;
        int i, iPixels, gray;
        build_lookup_table(iCount);
        // Take BITMAP structure from HBITMAP
        GetObject(*phBitmap, sizeof(BITMAP), &bm);
        // Calculate bytes to read
        wByteCount = bm.bmHeight * (2 * ((bm.bmWidth * bm.bmBitsPixel + 15) / 16));
        // Alocate momory for bits od pixels and get pointers
        pBits = (BYTE *) malloc(wByteCount);
        GetBitmapBits(*phBitmap, wByteCount, pBits);
        // Convert pointer to byte to pointer to RGBQUAD
        pRgb = (RGBQUAD *) pBits;
        // Operate on pixel's colors
        iPixels = wByteCount / (bm.bmBitsPixel / 8);
        for(int i = 0; i < iPixels; i++, pRgb++)
        {
            gray = (pRgb->rgbRed + pRgb->rgbGreen + pRgb->rgbBlue) / 3;
            int k = TransLut[gray]-gray;
            pRgb->rgbRed   = min(pRgb->rgbRed   + k, 255);
            pRgb->rgbGreen = min(pRgb->rgbGreen + k, 255);
            pRgb->rgbBlue  = min(pRgb->rgbBlue  + k, 255);
        }
        SetBitmapBits(*phBitmap, wByteCount, pBits);
        return TRUE;
    }
}

我不明白为什么我会收到这样的错误：

错误
1. C2061：语法错误：标识符"HBITMAP"CDLL.h
2. 错误 C2511："布尔 CDLL：：CDLL：：对比度（HBITMAP *，int）"：重载在"CDLL：：CDLL"中找不到成员函数
.cpp

#2 不是关于头文件中的方法声明吗？我应该如何解决这个问题？