Setting Up and Using Flex (Lex for Windows) with Visual C++ 6.0

I have written this HTML page for those who are interested in using the "lex" and "yacc" unix commands on Microsoft Windows machines. It is assumed that the reader has some knowledge (but not much) of the Visual C++ 6.0 integrated development environment.

The first thing you need to do is to download the necessary software. Although there are many clones available all over the web, the following link will download the files for you to build programs using Visual Studio 6.0: Click Here for Download the Flex and Bison Tools.

After you have downloaded the zip file from clicking the above link, extract all the files to a directory of your choice and then run the "setup.exe" file. This will install "Flex.exe" and "Bison.exe" on a Windows machine. The installation process will find the appropriate directories on your computer that house Visual Studio 6.0 and will install the necessary files into those directories.

Running the Lex Program:

For the sake of helpfulness, I will give an example assuming the "Flex.exe" program was installed in the "C:\Program Files\Microsoft Visual Studio\Common\Bin" directory. However, if you have a path to this directory predefined in your environmental variables, you won't need to type in the entire path to the "Flex.exe" program. Regardless of where the "Flex.exe" program is, if it is not defined as an environment variable then all you have to do is fill in the entire path to it in the appropriate places in the following example:

• Create the Lex specification file you will run against Lex. For the sake of our example, let's imagine that you call this file "HomeworkOne.l", and that it is located in the "C:\" directory.
• Open up a command line window and issue the following command (include quotation marks if your path contains whitespace): "C:\Program Files\Microsoft Visual Studio\Common\Bin\Flex" "C:\HomeworkOne.l". This command feeds the "HomeworkOne.l" file to the "Flex" program.
• If you would like to use C++ rather than c, use the -ooutput option, which will cause flex to create a file with a name of your choice instead of "lex.yy.c". If you choose a file name with a ".cpp" extension, it helps the Visual C++ compiler compile for C++ features. To use the -oouput option, substitute the name of the file you would like produced for output. For instance, if you want the file to be named "lex.yy.cpp", use the following command line input. Note that there are no spaces after the between the -o and the filename::
  • "C:\Program Files\Microsoft Visual Studio\Common\Bin\Flex" -olex.yy.cpp C:\HomeworkOne.l

The above steps should have created a "lex.yy.c" file or a "lex.yy.cpp" file, which we will now use to compile into an executable using Visual Studio 6.0

• Open up Visual Studio 6.0

• Create an empty project, and place the "lex.yy.c" or "lex.yy.cpp" file we created above into the top-level project directory.

• Add the "lex.yy.c" or "lex.yy.cpp" file to the project by clicking on "Project | Add to Project... | Add Files..." menu item, and then selecting the file.

• Click on the "Project | Settings..." menu item, and then click on the "Link" tab in the dialog box that appears.

• In the "Object/library modules:" text box, move the cursor to the end of the line, past all the other "lib" files, and add in the full path to the "LIBFLEX.lib" file that is found in the "lib" directory of the Flex and Bison installation you performed above. Surround the path with quotation marks to ensure that whitespaces in the path are taken into account.

• If you are compiling for C instead of C++, it appears as though you will need to add a couple of include directives in the definitions section of your input file or in the definition section of the "lex.yy.c" file.
  • #include <malloc.h>

  • #include <stdlib.h>

• Build the project. You might receive a LNK4098 warning if you are compiling for C, but disregard it. I haven't had the time to get rid of this warning, but it causes no harm.

• Feed a file you want to parse against the executable you created in the above step. If the executable is named "HomeworkOne.exe" and the file you want to parse is "C:\HomeworkOneParseFile.txt", then the command will be:

  • HomeworkOne < C:\HomeworkOneParseFile.txt

• To help ease the running of the program you have created so you don't have to use the command line every time, you can click on the "Project | Settings..." menu item, click on the "Debug" tab, and then supply the program arguments (in the case of our example, "< C:\HomeworkOneParseFile.txt".

I hope this helps!