Get size of a buffer in C#

Question

I have a C++/CLI dll and one of the methods requires a pointer and its buffer size as its parameters.

C++/CLI

• Param1:BufferPtr = Pointer to the beginning of the buffer.
• Param2:BufferSize = Size of the buffer.

---

// Example..
uint LoadImageFromMemory(const unsigned char * const  BufferPtr, const int BufferSize);

---

C#

Bitmap Img = Bitmap.FromFile(@"C:/my.jpg") as Bitmap;
.
.
// Convert the 'Img' to byte* pointer.
byte[] TempByte = new byte[TempStorage.Height * TempStorage.Width * 3];
byte[] ActualByte = null;

System.Drawing.Imaging.BitmapData m_pImageData = null;

// Converting Bitmap to Byte array...
try
{
     m_pImageData = TempStorage.LockBits(new Rectangle(0, 0, TempStorage.Width, TempStorage.Height),
                                             System.Drawing.Imaging.ImageLockMode.ReadWrite,
                                             System.Drawing.Imaging.PixelFormat.Format24bppRgb);

     System.IntPtr pScan = m_pImageData.Scan0; // 5
     int nStride = m_pImageData.Stride;// 6
     ActualByte = new byte[m_pImageData.Height * m_pImageData.Width * 3];

     unsafe
     {
          byte* pBuffer = (byte*)(void*)pScan;// 7

          int noffset = nStride - TempStorage.Width * 3;

          int count = 0;
          for (int nY = 0; nY < TempStorage.Height; nY++)
          {
               for (int nX = 0; nX < TempStorage.Width; nX++)
               {

                    ActualByte[count] = pBuffer[0];
                    ActualByte[count + 1] = pBuffer[1];
                    ActualByte[count + 2] = pBuffer[2];
                    count += 3;
                    pBuffer += 3;
               }
               pBuffer += noffset;
            }
        }
    }
finally
{
     if (m_pImageData != null)
     {
         TempStorage.UnlockBits(m_pImageData);
     }
}

.
.
// At the end... 
.
.
fixed (byte* ptrAdd = ActualByte)
{
                  // this second parameter ( below ) is problematic...
    rst = CppAPI.LoadImageFromMemory(ptrAdd, ?????);
}

---

How can I get the buffer size?

Since I have no idea of what exactly the buffer size means here, I tried to pass these values into the second parameter, wild-guessing.

• ActualByte length,
• Stride of this 'my.jpg' image
• The address value as an int ( A stupid wild guess ! )

Unfortunately, none of them worked.

I have the image, its bitmap object and its pointer in C#. Aren't these sufficient to get the buffer size?

Answer 1

After I read the comments Ken White mentioned, it comes into my mind that converting job itself could be wrong in the first place.

So I got rid of this code below

try
{
     m_pImageData = TempStorage.LockBits(new Rectangle(0, 0, TempStorage.Width, TempStorage.Height),
                                             System.Drawing.Imaging.ImageLockMode.ReadWrite,
                                             System.Drawing.Imaging.PixelFormat.Format24bppRgb);

     System.IntPtr pScan = m_pImageData.Scan0; // 5
     int nStride = m_pImageData.Stride;// 6
     ActualByte = new byte[m_pImageData.Height * m_pImageData.Width * 3];

     unsafe
     {
          byte* pBuffer = (byte*)(void*)pScan;// 7

          int noffset = nStride - TempStorage.Width * 3;

          int count = 0;
          for (int nY = 0; nY < TempStorage.Height; nY++)
          {
               for (int nX = 0; nX < TempStorage.Width; nX++)
               {

                    ActualByte[count] = pBuffer[0];
                    ActualByte[count + 1] = pBuffer[1];
                    ActualByte[count + 2] = pBuffer[2];
                    count += 3;
                    pBuffer += 3;
               }
               pBuffer += noffset;
            }
        }
    }
finally
{
     if (m_pImageData != null)
     {
         TempStorage.UnlockBits(m_pImageData);
     }
}

and decided to use MemoryStream instead.

using (MemoryStream ms = new MemoryStream())
{
    Img.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
    ActualByte = ms.ToArray();
}

It works fine now and the second parameter value was supposed to be the byte array length, as Ken White said in his comment.

// This should be...
CppAPI.LoadImageFromMemory(ptrAdd, ?????);

// Like this..
CppAPI.LoadImageFromMemory(ptrAdd, ActualByte.length);

Answer 2

You defined the array as a byte array, so it is exactly as large as you defined it. m_pImageData.Height * m_pImageData.Width * 3 bytes long.