As a supporter of the GNU Project, I am not so happy to use DISLIN, which comes with an EULA, but I don’t have time to find out another alternative to the plotting library suggested by Prof. Yevick in a book.¹

A DISLIN installation guide on Ubuntu was written more than six years ago, so I am a bit dubious that if steps 2 and 3 are still needed for the installation using a DEB file.² Therefore, I overlooked an important command and I regret this after wasting about two hours on Google.

As a result, I just downloaded the DEB file from the DISLIN official website and use the GUI tool “Ubuntu Software Centre” to install the library. Then I directly copied the code from the book and tried to compile the program .

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// Author: David Yevick
// Source: A Short Course in Computational Science and Engineering
#include <iostream>
#include <dislin.h>

using namespace std;

int main(int argc, const char *argv[])
{
    // Some code for defining variables
    // Omitted to avoid copyright problems
    // An example of using DISLIN methods
    qplot(array1,array2,numOfPts);
}

However, the compiler gave me the message that I had used an “undefined reference to qplot”.

I googled for two hours and found nothing that I can understand. I even tried compiling the following sample code found in section 2.7 of the official DISLIN online manual.

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// Author: Helmut Michels
// Source: DISLIN 10.4—A Data Plotting Library
#include <iostream>
#include "discpp.h"

main()
{
    Dislin g;
    g.disini ();
    g.messag ("This is a test", 100, 100);
    g.disfin ();
}

I have no hope on published books because their authors would expect their students to do something easy—Use Dev-C++ on M$ Win*, or *nix GUI IDE like Eclipse. However, some geeks won’t be satisfied because GUI buttons/objects hide the commands away from users. As a result, they don’t know what tasks are invoked by clicking the button/object. In other words, they don’t know what they are actually doing. Therefore, they have the motivation to find out the real command for the compilation of C++ programs that #include "dislin.h".

Stack Overflow has a few or no questions on the compilation of C++ programs that use DISLIN. The most relevant one that I managed to find is question 19118465. I glanced at the answers quickly. They have some commands like

$ gfortran EX11_1.f90 -o progrname -ldislin -I/path/to/DISLIN/modules

Then I guessed that I need the -ldislin flag as well. I can’t truly figure out the usage of -l, -L and -I flags by just looking at the man page of g++, so I just tried everything. I searched for some new pages, and returned to some web pages that I’ve already visited, and continued this unproductive process…

I googled the websites and I saw the post on Linux for Research mentioned before. I looked at the command that begins with g++ and tried to adapt it to my needs, but it simply failed.

I thought that the official README maybe useful, so I browsed the contents in /usr/local/dislin/README. Some websites that teach users to install DISLIN from a gzip tarball contain code that manipulate the environment variables like DISLIN, PATH and LD_LIBRARY_PATH. But in the README, it’s clearly stated that I don’t need to do so.

f) To make DISLIN available for general use, write the following com-
mands to your .profile or to /etc/profile

DISLIN=directory
export DISLIN
PATH=${PATH}:${DISLIN}/bin

LD_LIBRARY_PATH=$DISLIN:$LD_LIBRARY_PATH
export LD_LIBRARY_PATH

Note: The environment variable DISLIN is not necessary if DISLIN
is installed in the default directory '/usr/local/dislin'.

I think that I don’t need to do the above settings, but I am not sure about that. Luckily, the following part that immediately follows the above section gave me some hint on what I, as a newcomer to DISLIN, can do.

4.) Compiling, Linking and Running the Example Programs

    Now you can compile, link and run the example programs in the
    directory $DISLIN/examples with the commands:

		    clink     -a exa_c      (for gcc)
		    cpplink   -a exa_cpp    (for g++)
		    iclink    -a exa_c      (for Intel icc)
		    sclink    -a exa_c      (Sun Studio cc)
...

Thus, I really went to /usr/local/dislin/example and compiled exa_cpp.cpp using cpplink with the -a flag. It works! No complaints from g++! It seemed that I could give cpplink a try, but it quickly turned out that my idea failed to work. g++ either complained that dislin.h was not found, or there’s “undefined reference” to a DISLIN function.

After that, I returned to Google again, and was redirected to the same post on Linux for Research again. I glanced through the same command that started with g++.

$ g++ test.cpp -lXt -ldislin -lm

This time, I could read the sentence below the above command.

Don't forget the `-lXt`

I finally realised that I had forgotten an important principle in programming: Don’t do too much at one time. At the very first stage, I need to get things done, though the approach is not elegant.

With the above principle in my mind, I could merely compile a C++ program that made use of DISLIN by making the following changes in both the source file and the command that I issued.

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// Author: David Yevick
// Source: A Short Course in Computational Science and Engineering
#include <iostream>
#include "/usr/local/dislin/dislin.h"

using namespace std;

int main(int argc, const char *argv[])
{
// Some code for defining variables
// Omitted to avoid copyright problems
// An example of using DISLIN methods
qplot(array1,array2,numOfPts);
}

In the terminal, I typed the following command.

$ g++ foo.cpp -lXt -ldislin -lm

It works! Critical readers will complain about the way that I include dislin.h. I’m not satisfied with this either. Another obvious missing part for those who want to customise the name of the output executable file is the -o flag. I delibrately did this so as to keep things simple and clear.

After trying the -l, -L and -I flags of the command g++, I realised that the -I flag will do.

However, when I tried to do the same task for another time, it surprisingly failed. Looking closely at the two versions, we can draw the following conclusion.

# `DISLIN' is a variable that represents the path of DISLIN.
# In the default case, it is `/usr/local/dislin'.
$ g++ -lXt -ldislin -lm -I$(DISLIN) foo.cpp -o foo.out # Wrong!
$ g++ foo.cpp -o foo.out -lXt -ldislin -lm -I$(DISLIN) # Correct!

I conclude this post with the fact that the flags -g -Wall can be put either before or after foo.cpp.

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