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AutoCAD File Format, Read and Write DXF drawing with Visual C++ Source Code


What is Auto CAD DXF?

Drawing Interchange Format (DXF) files enable the interchange of drawings between AutoCAD and other programs. DXF files can be either ASCII or binary formats. Because ASCII DXF files are more common than the binary format, CadLib uses ASCII DXF format.

What is CadLib?

The CadLib is not a Computer Aided Design (CAD) program. It is a tool for creating DXF files that are used in the CAD programs. It consists of two parts. One of them is a Dynamic Link Library to create the DXF file. The other part is the programming interface. It is a class that integrates the cadio.dll functions. It can be used in Microsoft Visual C++ projects. In addition, the cadio.dll can be used in other Win32 programs.

Why use CadLib?

In some programs, it is needed to create a drawing output for use in other programs such as AutoCad. For example, in a "Building Detail Sheet Generator Program", the program needs to create a drawing output. And the most standard format for communicating drawing data is DXF.

DXF file structure

The DXF format is a tagged data representation of all the information contained in a drawing file. Tagged data means that each data element in the file is preceded by an integer number that is called a group code. A group code's value indicates what type of data element follows. This value also indicates the meaning of a data element for a given object (or record) type. Virtually all user-specified information in a drawing file can be represented in DXF format. (from AutoCad's DXF reference)

A DXF file consists of some sections. Each section has some drawing data in itself. The CadLib uses the following sections:


The main reference for DXF file structure that is used for CadLib is the AutoCad's DXF reference. You can find more information about DXF file structure here.


The classes are interfaces between CadIO.dll and the main program. "Test" has come with CadLib to demonstrate how to generate a DXF file with CDxfFileWrite and CDrawing classes.

CDxfFileWrite class

CDxfFileWrite gathers all the commands needed to directly create a DXF file. Usage of CDxfFileWrite is as follows:

  1. Create the DXF file
    CDxfFileWrite dxffile;
    dxffile.Create( "d:\\test.dxf" );
  2. Begin and end the HEADER section. It's here for compatibility with some CAD programs. Others work without having HEADER section.
    // Header Section ------------------------------------------
    // close HEADER section ------------------------------------
  3. Begin the TABLES section and put the LAYER, LTYPE, STYLE, DIMSTYLE table-types as many as you want and then close the section
    // Tables Section ------------------------------------------
    // LTYPE table type -------------------------
    DXFLTYPE ltype;
    double elem[4];
    // Continuous
    ZeroMemory(<ype, sizeof(ltype));
    ltype.Name = "Continuous";
    ltype.DescriptiveText = "Solid line";
    // DASHDOT2
    ZeroMemory(<ype, sizeof(ltype));
    ltype.Name = "DASHDOT2";
    ltype.DescriptiveText = "Dash dot (.5x) _._._._._._._._._._._._._._._.";
    ltype.ElementsNumber = 4;
    ltype.TotalPatternLength = 0.5;
    ltype.Elements = elem;
    elem[0] = 0.25;
    elem[1] = -0.125;
    elem[2] = 0.0;
    elem[3] = -0.125;
    // close LTYPE table type -------------------
    // LAYER table type -------------------------
    result &= dxffile.BeginTableType(TAB_LAYER);
    result &= dxffile.AddLayer("Layer1", 1, "Continuous");
    result &= dxffile.AddLayer("Layer2", 2, "Continuous");
    result &= dxffile.AddLayer("Layer3", 3, "Continuous");
    result &= dxffile.AddLayer("Layer4", 4, "Continuous");
    result &= dxffile.EndTableType();
    // close LAYER table type -------------------
    // STYLE table type -------------------------
    DXFSTYLE tstyle;
    ZeroMemory(&tstyle, sizeof(tstyle));
    tstyle.Name = "Style1";
    tstyle.PrimaryFontFilename = "TIMES.TTF";
    tstyle.Height = 0.3;
    tstyle.WidthFactor = 1;
    // close STYLE table type -------------------
    // DIMSTYLE table type ----------------------
    DXFDIMSTYLE dimstyle;
    // DIM1
    ZeroMemory(&dimstyle, sizeof(dimstyle));
    dimstyle.Name = "DIM1"; // DimStyle Name
    dimstyle.DIMCLRD = 2; // Dimension line & Arrow heads color
    dimstyle.DIMDLE = 0.0000; // Dimension line size after Extensionline
    dimstyle.DIMCLRE = 2; // Extension line color
    dimstyle.DIMEXE = 0.1800; // Extension line size after Dimline
    dimstyle.DIMEXO = 0.0625; // Offset from origin
    dimstyle.DIMBLK1 = "ClosedFilled";// 1st Arrow head
    dimstyle.DIMBLK2 = "ClosedFilled";// 2nd Arrow head
    dimstyle.DIMASZ = 0.1800; // Arrow size
    dimstyle.DIMTXSTY = "Style1"; // Text style
    dimstyle.DIMCLRT = 3; // Text color
    dimstyle.DIMTXT = 0.1800; // Text height
    dimstyle.DIMTAD = 1; // Vertical Text Placement
    dimstyle.DIMGAP = 0.0900; // Offset from dimension line
    // close DIMSTYLE table type ----------------
    // close TABLES section ------------------------------------
  4. Begin ENTITIES section and put entities data (LINE, CIRCLE, SOLID, TEXT, ARC, POINT, DIMLINEAR) and finally close the section
    // Entities Section ------------------------------------------
    // set current layer to Layer2
    // draw a line
    dxffile.Line(1.2, 3.3, 7.5, 7.7);
    // draw a circle
    dxffile.Circle(7.8, 4.3, 1.75);
    // set current layer to Layer4
    // draw a solid
    REALPOINT points[4];
    points[0].x = 10.4; points[0].y = 7.2;
    points[1].x = 13.6; points[1].y = 7.4;
    points[2].x = 13.1; points[2].y = 4.9;
    points[3].x = 10.9; points[3].y = 5.9;
    Solid(4, points);
    // set current textstyle to Style1
    // draw text
    dxffile.Text("Sample Text", 5.9, 6.7, 0.3, 35);
    // draw a dimension line
    dxffile.DimLinear(6.05, 3, 9.55, 3, 9.55, 2, 0, "3.50");
    // close ENTITIES section ----------------------------------
  5. Close the DXF file

CDrawing class

CDrawing class has all the commands to create a drawing in memory and save it as a DXF file. Usage of CDrawing is as follows:

  1. Create the on-memory drawing
    CDrawing drw;
    drw.Create( );
  2. Create new LAYER, LTYPE, STYLE, DIMSTYLE table-types as many as you want.
    // Tables Section ------------------------------------------
    // LTYPE table type -------------------------
    LTYPE ltype;
    OBJHANDLE objhandle1;
    // Continuous
    ZeroMemory(<ype, sizeof(ltype));
    strcpy(ltype.Name, "Continuous");
    strcpy(ltype.DescriptiveText, "Solid line");
    objhandle1 = drw.AddLinetype(<ype);
    // DASHDOT2
    ZeroMemory(<ype, sizeof(ltype));
    strcpy(ltype.Name, "DASHDOT2");
      "Dash dot (.5x) _._._._._._._._._._._._._._._.");
    ltype.ElementsNumber = 4;
    ltype.PatternLength = 0.5;
    ltype.Elements[0] = 0.25;
    ltype.Elements[1] = -0.125;
    ltype.Elements[2] = 0.0;
    ltype.Elements[3] = -0.125;
    // LAYER table type -------------------------
    LAYER layer;
    // Layer1
    ZeroMemory(&layer, sizeof(layer));
    strcpy(layer.Name, "Layer1");
    layer.Color = 1;
    layer.LineTypeObjhandle = objhandle1; // Continuous
    // Layer2
    ZeroMemory(&layer, sizeof(layer));
    strcpy(layer.Name, "Layer2");
    layer.Color = 2;
    layer.LineTypeObjhandle = objhandle1; // Continuous
    // STYLE table type -------------------------
    STYLE style;
    ZeroMemory(&style, sizeof(style));
    strcpy(style.Name, "Style1");
    strcpy(style.PrimaryFontFilename, "TIMES.TTF");
    style.LastHeightUsed = 0.3;
    style.WidthFactor = 1;
    objhandle1 = drw.AddTextStyle(&style);
    // DIMSTYLE table type ----------------------
        DIMSTYLE dimstyle;
    // DIM1
    ZeroMemory(&dimstyle, sizeof(dimstyle));
    strcpy(dimstyle.Name, "DIM1"); // DimStyle Name
    dimstyle.dimclrd = 2; // Dimension line & Arrow heads color
    dimstyle.dimdle = 0.0000; // Dimension line size after Extensionline
    dimstyle.dimclre = 2; // Extension line color
    dimstyle.dimexe = 0.1800; // Extension line size after Dimline
    dimstyle.dimexo = 0.0625; // Offset from origin
    strcpy(dimstyle.dimblk1, "ClosedFilled");// 1st Arrow head
    strcpy(dimstyle.dimblk2, "ClosedFilled");// 2nd Arrow head
    dimstyle.dimasz = 0.1800; // Arrow size
    dimstyle.dimtxstyObjhandle = objhandle1;// Text style
    dimstyle.dimclrt = 3; // Text color
    dimstyle.dimtxt = 0.1800; // Text height
    dimstyle.dimtad = 1; // Vertical Text Placement
    dimstyle.dimgap = 0.0900; // Offset from dimension line
    // Entities Section ------------------------------------------
    // set current layer to Layer2
    // draw a line
    drw.Line(1.2, 3.3, 7.5, 7.7);
    // draw a circle
    drw.Circle(7.8, 4.3, 1.75);
    // set current layer to Layer1
    // draw a solid
    REALPOINT points[4];
    points[0].x = 10.4; points[0].y = 7.2;
    points[1].x = 13.6; points[1].y = 7.4;
    points[2].x = 13.1; points[2].y = 4.9;
    points[3].x = 10.9; points[3].y = 5.9;
    drw.Solid(points[0], points[1], points[2], points[3]);
    // set current textstyle to Style1
    // draw text
    drw.Text("Sample Text", 5.9, 6.7, 0.3, 35);
    // draw a dimension line
    drw.DimLinear(6.05, 3, 9.55, 3, 9.55, 2, 0, "3.50");
  4. Save data to a DXF file.
  5. Destroy CDrawing and free allocated memory.

Loading data from a DXF file

  1. Create the on-memory drawing.
    CDrawing drw;
    drw.Create( );
  2. Use LoadDXFFile member function to load DXF file into memory.

That's all!


Since I am a Civil Engineer, I decided to write a program to generate a beam or columns detail sheet without the use of AutoCAD. I have written a program that, with a little data about beam or column, will create the detail sheet automatically. Output of this program is a DXF file and it can be shown in AutoCAD or it can be plotted with it. This program can save the time for drawing the detail sheet with AutoCAD. If you are an AutoCAD operator, you will understand the meaning of words that are used in this article, or if you are a programmer who wants to write a program to create DXF files, first you need a little knowledge about AutoCAD or the drawing programs such as is mentioned above. This code can be useful for programmers who need to create DXF files from their programs. CadLib is not the best one and also there are many commercial software for creating DXF files but they are not open source. Feel free to change the code. Your comments in regards to this article will cause the improvement of CadLib.


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