<title>18. Abbreviations</title>

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<table class="contents"><tr><td>

<h4>Contents</h4>

<div><a href="htpataic01.html">1. Introduction</a></div>

<div><a href="htpataic02.html">2. The main loop</a></div>

<div><a href="htpataic03.html">3. Locations</a></div>

<div><a href="htpataic04.html">4. Objects</a></div>

<div><a href="htpataic05.html">5. Inventory</a></div>

<div><a href="htpataic06.html">6. Passages</a></div>

<div><a href="htpataic07.html">7. Distance</a></div>

<div><a href="htpataic08.html">8. North, east, south, west</a></div>

<div><a href="htpataic09.html">9. Code generation</a></div>

<div><a href="htpataic10.html">10. More attributes</a></div>

<div><a href="htpataic11.html">11. Conditions</a></div>

<div><a href="htpataic12.html">12. Open and close</a></div>

<div><a href="htpataic13.html">13. The parser</a></div>

<div><a href="htpataic14.html">14. Multiple nouns</a></div>

<div><a href="htpataic15.html">15. Light and dark</a></div>

<div><a href="htpataic16.html">16. Savegame</a></div>

<div><a href="htpataic17.html">17. Test automation</a></div>

<div><b>18. Abbreviations</b></div>

<div><a href="htpataic19.html">19. Conversations</a></div>

<div><a href="htpataic20.html">20. Combat</a></div>

<div><a href="htpataic21.html">21. Multi-player</a></div>

<div><a href="htpataic22.html">22. Client-server</a></div>

<div><a href="htpataic23.html">23. Database</a></div>

<div><a href="htpataic24.html">24. Speech</a></div>

<div><a href="htpataic25.html">25. JavaScript</a></div>

<h1>How to program a text adventure in C</h1>

by Ruud Helderman

&lt;<a href="mailto:r.helderman@hccnet.nl">r.helderman@hccnet.nl</a>&gt;

Licensed under

<a href="https://github.com/helderman/htpataic/blob/master/LICENSE">MIT License</a>

<h2>18. Abbreviations</h2>

<p class="intro">

Classic adventures like

<a href="https://en.wikipedia.org/wiki/Colossal_Cave_Adventure">Colossal Cave</a>

and

<a href="https://en.wikipedia.org/wiki/Zork">Zork</a>

have more than a hundred locations for the player to discover.

Playing these games involves a lot of &ldquo;go north/east/south/west&rdquo;,

so it&rsquo;s no surprise that from the very beginning,

text adventures accepted abbreviations like n, e, s, w.

Implementing an abbreviation appears to be trivial.

From a coding perspective,

an abbreviation is just a synonym for its full-sized counterpart, right?

So all we have to do is

add an extra row to the list of commands in function <i>parseAndExecute</i>.

There is a downside to that approach. When using

<a href="https://en.wikipedia.org/wiki/Speech_synthesis">text-to-speech</a>

to read out loud the progress of a game session,

those abbreviations do not come out too well.

How is a

<a href="https://en.wikipedia.org/wiki/Screen_reader">screen reader</a>

supposed to know &lsquo;ne&rsquo; means north-east?

So instead, I would recommend a pre-processor that

<b>expands</b> abbreviations before sending the user&rsquo;s input to the parser.

Implementation-wise,

such a pre-processor is quite similar to the actual parser.

We can even re-use function <i>matchCommand</i>.

It may seem like overkill to use <i>matchCommand</i>

for recognizing a one-letter command like &lsquo;n&rsquo;,

but why would I want to implement

case insensitivity and whitespace trimming all over again?

One may argue that this approach is suboptimal.

A simple abbreviation is expanded to something more verbose

(e.g. &ldquo;go north&rdquo;),

which then has to be broken down again by the parser.

Please feel free to optimize, if it makes you feel better.

Just remember the

<a href="http://wiki.c2.com/?RulesOfOptimization">rules of optimization</a>

from the previous chapter.

<table class="code"><tr>

<th>expand.h</th>

<li class="new">extern char *expand(char *input, int bufsize);</li>

<th>expand.c</th>

<li class="new">#include &lt;stdbool.h&gt;</li>

<li class="new">#include &lt;string.h&gt;</li>

<li class="new">#include "match.h"</li>

<li class="new"></li>

<li class="new">typedef struct</li>

<li class="new">{</li>

<li class="new"> const char *abbreviated;</li>

<li class="new"> const char *expanded;</li>

<li class="new">} SHORTHAND;</li>

<li class="new"></li>

<li class="new">static int minimum(int x, int y)</li>

<li class="new">{</li>

<li class="new"> return x &lt; y ? x : y;</li>

<li class="new">}</li>

<li class="new"></li>

<li class="new">char *expand(char *input, int bufsize)</li>

<li class="new">{</li>

<li class="new"> static const SHORTHAND shorthands[] =</li>

<li class="new"> {</li>

<li class="new"> {"n", "go north"},</li>

<li class="new"> {"s", "go south"},</li>

<li class="new"> {"w", "go west"},</li>

<li class="new"> {"e", "go east"},</li>

<li class="new"> {"inv", "inventory"},</li>

<li class="new"> {"x A", "examine "},</li>

<li class="new"> {"A", NULL}</li>

<li class="new"> };</li>

<li class="new"> const SHORTHAND *sh;</li>

<li class="new"> for (sh = shorthands; !matchCommand(input, sh-&gt;abbreviated); sh++);</li>

<li class="new"> if (sh-&gt;expanded != NULL)</li>

<li class="new"> {</li>

<li class="new"> const char *moreInput = *paramByLetter('A');</li>

<li class="new"> int lengthOfExpanded = strlen(sh-&gt;expanded);</li>

<li class="new"> memmove(input + lengthOfExpanded, moreInput,</li>

<li class="new"> minimum(strlen(moreInput) + 1, bufsize - lengthOfExpanded - 1));</li>

<li class="new"> strncpy(input, sh-&gt;expanded, lengthOfExpanded);</li>

<li class="new"> }</li>

<li class="new"> return input;</li>

<li class="new">}</li>

<div class="explanation">

Explanation:

<li>Line 5-9:

struct <i>SHORTHAND</i> is similar to struct <i>COMMAND</i>

(defined in <i>parsexec.c</i>).

It maps a command pattern not to a function

but to another (more verbose) command string.

<li>Line 16:

this is the function that expands the abbreviation (if any).

Expansion takes place directly in the input buffer.

To be able to prevent

<a href="http://en.wikipedia.org/wiki/Buffer_overflow">buffer overflow</a>,

the function must be aware of the size of the buffer

(parameter <i>bufsize</i>).

<li>Line 25:

an example of an expansion that is slightly less trivial.

When expanding &lsquo;x&rsquo; to &lsquo;examine&rsquo;,

we should preserve whatever follows the verb.

For example,

&ldquo;x coin&rdquo; should be expanded to &ldquo;examine coin&rdquo;.

The trailing space in the string &ldquo;examine &rdquo; is there on purpose;

it helps to keep the code simple.

<li>Line 26:

just like in the parser, the final pattern &ldquo;A&rdquo;

should catch every command that did not match any of the abbreviations.

<li>Line 29:

this loop tries to find the abbreviation that matches the user&rsquo;s input.

<li>Line 30:

if the loop stopped at the final &lsquo;sure-match&rsquo; pattern (line 26),

then there was no matching abbreviation.

We will skip the rest of the function; no expansion will take place.

<li>Line 32:

retrieves the value of parameter <i>A</i>

(e.g. &ldquo;coin&rdquo; if the user entered &ldquo;x coin&rdquo;),

or an empty string if the abbreviation is parameterless.

<li>Line 34:

moving the noun (the parameter <i>A</i>, if any) away from the verb,

to make room for the expanded verb.

Deliberately using <i>memmove</i> instead of <i>strcpy</i>

(from <a href="http://en.wikipedia.org/wiki/String.h">string.h</a>),

as we are (possibly) moving data within the same input buffer.

<li>Line 35:

here <i>bufsize</i> is taken into account, to prevent

<a href="http://en.wikipedia.org/wiki/Buffer_overflow">buffer overflow</a>.

For very long commands, this may truncate the string,

but assuming the buffer has a reasonable size,

that is unlikely to bother the player.

<li>Line 36:

now we can finally copy the expanded command to the front of the input buffer.

Now all we have to do is call function <i>expand</i>

right before calling <i>parseAndExecute</i>.

<table class="demo">

<tr><th>Sample output</th></tr>

Welcome to Little Cave Adventure.<br />

You are in an open field.<br />

You see:<br />

a silver coin<br />

a burly guard<br />

a cave entrance to the east<br />

dense forest all around<br />

a lamp<br />

<br />

--&gt; e<br />

The guard stops you from walking into the cave.<br />

<br />

--&gt; get coin<br />

You pick up a silver coin.<br />

<br />

--&gt; inv<br />

You have:<br />

a silver coin<br />

<br />

--&gt; x coin<br />

The coin has an eagle on the obverse.<br />

<br />

--&gt; give coin<br />

You give a silver coin to a burly guard.<br />

<br />

--&gt; e<br />

You walk into the cave.<br />

<br />

It is very dark in here.<br />

You see:<br />

an exit to the west<br />

<br />

--&gt; n<br />

It's too dark.<br />

<br />

--&gt; w<br />

You walk out of the cave.<br />

<br />

You are in an open field.<br />

You see:<br />

a burly guard<br />

a cave entrance to the east<br />

dense forest all around<br />

a lamp<br />

<br />

--&gt; w<br />

Dense forest is blocking the way.<br />

<br />

--&gt; quit<br />

<br />

Bye!<br />

<table class="code"><tr>

<th>main.c</th>

<li class="old">#include &lt;stdbool.h&gt;</li>

<li class="old">#include &lt;stdio.h&gt;</li>

<li class="old">#include &lt;string.h&gt;</li>

<li class="new"><span class="old">#include </span>"expand.h"</li>

<li class="new">#include<span class="old"> "parsexec.h"</span></li>

<li class="old"></li>

<li class="old">static char input[100] = "look around";</li>

<li class="old"></li>

<li class="old">static bool getFromFP(FILE *fp)</li>

<li class="old">{</li>

<li class="old"> bool ok = fgets(input, sizeof input, fp) != NULL;</li>

<li class="old"> if (ok) input[strcspn(input, "\n")] = '\0';</li>

<li class="old"> return ok;</li>

<li class="old">}</li>

<li class="old"></li>

<li class="old">static bool getInput(const char *filename)</li>

<li class="old">{</li>

<li class="old"> static FILE *fp = NULL;</li>

<li class="old"> bool ok;</li>

<li class="old"> if (fp == NULL)</li>

<li class="old"> {</li>

<li class="old"> if (filename != NULL) fp = fopen(filename, "rt");</li>

<li class="old"> if (fp == NULL) fp = stdin;</li>

<li class="old"> }</li>

<li class="old"> else if (fp == stdin &amp;&amp; filename != NULL)</li>

<li class="old"> {</li>

<li class="old"> FILE *out = fopen(filename, "at");</li>

<li class="old"> if (out != NULL)</li>

<li class="old"> {</li>

<li class="old"> fprintf(out, "%s\n", input);</li>

<li class="old"> fclose(out);</li>

<li class="old"> }</li>

<li class="old"> }</li>

<li class="old"> printf("\n--&gt; ");</li>

<li class="old"> ok = getFromFP(fp);</li>

<li class="old"> if (fp != stdin)</li>

<li class="old"> {</li>

<li class="old"> if (ok)</li>

<li class="old"> {</li>

<li class="old"> printf("%s\n", input);</li>

<li class="old"> }</li>

<li class="old"> else</li>

<li class="old"> {</li>

<li class="old"> fclose(fp);</li>

<li class="old"> ok = getFromFP(fp = stdin);</li>

<li class="old"> }</li>

<li class="old"> }</li>

<li class="old"> return ok;</li>

<li class="old">}</li>

<li class="old"></li>

<li class="old">int main(int argc, char *argv[])</li>

<li class="old">{</li>

<li class="old"> (void)argc;</li>

<li class="old"> printf("Welcome to Little Cave Adventure.\n");</li>

<li class="new"><span class="old"> while </span>(parseAndExecute(expand(input, sizeof input))<span class="old"> &amp;&amp; getInput(argv[1]));</span></li>

<li class="old"> printf("\nBye!\n");</li>

<li class="old"> return 0;</li>

<li class="old">}</li>

Of course, there should be more to an adventure than

traversing dozens of locations just to take object A to location B.

In the next chapter, we will look at ways to bring more depth into the game.

<hr />

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Next chapter: <a href="htpataic19.html">19. Conversations</a>