SFOParser.saveSFO C# (CSharp) Method

    public void saveSFO()
    {
        BinaryWriter bw = new BinaryWriter(new FileStream(filePath, FileMode.Open));
        byte[] tmpBuffer;
        GCHandle handle;
        psfHdr.label_ptr = Marshal.SizeOf(typeof(PsfHdr)) + psfHdr.nsects * Marshal.SizeOf(typeof(PsfSec));
        // write label Field
        bw.BaseStream.Position = psfHdr.label_ptr;
        for (int i = 0; i < psfHdr.nsects; i++) {
            psfSec[i].label_off = (short)(bw.BaseStream.Position - psfHdr.label_ptr);
            char []charBuffer = new char[pairs[i].label.Length+1];
            Array.Copy(pairs[i].label.ToCharArray(), charBuffer, pairs[i].label.Length);
            bw.Write(charBuffer);
        }

        // aline to 16byte
        int tmp = (int)(bw.BaseStream.Position % 16);
        if (tmp != 0) {
            psfHdr.data_ptr = (int)bw.BaseStream.Position + 16 - tmp;
        }
        psfHdr.data_ptr = (int)bw.BaseStream.Position;

        // write data set
        for (int i = 0, current_offset = 0; i < psfHdr.nsects; i++) {
            psfSec[i].data_off = current_offset;
            bw.BaseStream.Position = psfSec[i].data_off + psfHdr.data_ptr;
            switch (psfSec[i].data_type) {
                case 0:
                    tmpBuffer = (byte[])pairs[i].value;
                    break;
                case 2:
                    tmpBuffer = encode.GetBytes((string)pairs[i].value);
                    break;
                case 4:
                    tmpBuffer = BitConverter.GetBytes((int)pairs[i].value);
                    break;
                default:
                    tmpBuffer = (byte[])pairs[i].value;
                    break;
            }
            psfSec[i].datafield_used = tmpBuffer.Length;

            if (psfSec[i].datafield_size < psfSec[i].datafield_used) { // 對齊4byte
                tmp = (int)(psfSec[i].datafield_used % 4);
                if (tmp != 0) {
                    psfSec[i].datafield_size = (int)psfSec[i].datafield_used + 4 - tmp;
                } else {
                    psfSec[i].datafield_size = psfSec[i].datafield_used;
                }
            }

            char []clear_buf = new char[psfSec[i].datafield_size];
            bw.Write(clear_buf);
            bw.BaseStream.Position = psfSec[i].data_off + psfHdr.data_ptr;
            bw.Write(tmpBuffer);
            current_offset += psfSec[i].datafield_size;

        }

        // write psfSec, and get new data_ptr offset
        bw.BaseStream.Position = Marshal.SizeOf(typeof(PsfHdr));
        for (int i = 0; i < psfHdr.nsects; i++) {
            tmpBuffer = new byte[Marshal.SizeOf(typeof(PsfSec))];
            handle = GCHandle.Alloc(tmpBuffer, GCHandleType.Pinned);
            Marshal.StructureToPtr(psfSec[i], handle.AddrOfPinnedObject(), false);
            handle.Free();
            bw.Write(tmpBuffer);
        }
        psfHdr.label_ptr = (int)bw.BaseStream.Position;

        // write psfHdr
        bw.BaseStream.Position = 0;
        tmpBuffer = new byte[Marshal.SizeOf(typeof(PsfHdr))];
        handle = GCHandle.Alloc(tmpBuffer, GCHandleType.Pinned);
        Marshal.StructureToPtr(psfHdr, handle.AddrOfPinnedObject(), false);
        handle.Free();
        bw.Write(tmpBuffer);

        bw.Close();
    }

 private void saveToolStripMenuItem_Click(object sender, EventArgs e)
 {
     foreach (ListViewItem lvi in listViewEx1.Items)
     {
         if (m_sfo.getType((int)lvi.Tag) == (byte)SFOParser.SFOType.String && lvi.SubItems[1].Text[lvi.SubItems[1].Text.Length - 1] != '\0')
         {
             lvi.SubItems[1].Text += '\0';
         }
         m_sfo.setLabel((int)lvi.Tag, lvi.SubItems[0].Text);
         m_sfo.setValue((int)lvi.Tag, lvi.SubItems[1].Text);
     }
     m_sfo.saveSFO();
     MessageBox.Show(Resources.strings.File_saved);
 }