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authorTobias Klauser <tklauser@distanz.ch>2008-01-27 11:37:44 +0100
committerTobias Klauser <tklauser@xenon.tklauser.home>2008-01-27 11:37:44 +0100
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+<title>Strings</title>
+<body bgcolor="#ffffcc">
+<hr>
+<center><h1>Strings.</h1></center>
+<hr>
+<p>
+<h2>Pointers to strings.</h2>
+
+C does not have a "string" <a href=data_types.html>datatype</a>.
+To create a string you have to use a <a href=arrays.html#char>char array</a>
+or a <a href=data_types.html#char>char</a> pointer.
+If you are not familur with <a href=arrays.html#char>char arrays</a>
+I recomend that you read about them now.
+<p>
+To recap, a <a href=data_types.html#char>char</a> pointer is
+<a href=../glossary.html#definitions>defined</A> like this:
+<p>
+<table border=2 width=100% bgcolor=ivory>
+<tr><td>
+<pre>
+
+ main()
+ {
+ char *Text;
+ }
+
+</pre>
+</td></tr>
+</table>
+<p>
+
+All this program does is reserve storage that will hold an address.
+At this point the address could be anything. To initalize <b>Text</b>
+you can code:
+<p>
+<table border=2 width=100% bgcolor=ivory>
+<tr><td>
+<pre>
+
+ main()
+ {
+ char *Text = "Thunder";
+ }
+
+</td></tr></table>
+</pre>
+
+<b>Text</b> now has the address of the first character in <b>Thunder</B>.
+Graphically, things look like this.
+
+<pre>
+
+ (Address) (Data)
+
+ ---- ----
+ | F1 | 00 <------- Text
+ |----|----| (Data) (Adress)
+ | F2 | 00 | -------------
+ |----|----| -------> 54 (T) | D1 |
+ | F3 | 00 | | |--------|----|
+ |----|----| *Text | | 68 (h) | D2 |
+ | F4 | D1 | ------- |--------|----|
+ --------- | 75 (u) | D3 |
+ |--------|----|
+ | 6E (n) | D4 |
+ |--------|----|
+ | 64 (d) | D5 |
+ |--------|----|
+ | 65 (e) | D6 |
+ |--------|----|
+ | 72 (r) | D7 |
+ |--------|----|
+ | 00 | D8 |
+ -------------
+
+</pre>
+<p>
+
+Please note the <b>00</b> at the end of <b>Thunder</b>. This is
+the <a href=../SYNTAX/null.html>NULL</a> character and is used to mark the
+end of a string.
+<p>
+If we wanted to O/P the data pointed to by a <b>char pointer</b>
+ we can code.
+<p>
+<table border=2 width=100% bgcolor=ivory>
+<tr align=center><td>
+<b>Source</b>
+</td></tr><tr><td>
+<pre>
+
+ main()
+ {
+ char *Text1 = "Thunder"; /* Define and initalize */
+ char *Text2; /* Define only */
+
+ Text2 = "Bird"; /* Point to some text */
+
+ <a href=../FUNCTIONS/printf.html>printf</a>("%s%s\n", Text1, Text2);
+ }
+
+</pre>
+</td></tr>
+<tr align=center><td>
+<b>Result</b>
+</td></tr><tr><td>
+<pre>
+
+ ThunderBird
+
+</pre>
+</td></tr></table>
+<p>
+
+This is all very well, but there is a MAJOR problem! <b>Thunder</b>
+and <b>Bird</b> are
+<a href=constants.html>constants</a>, they cannot be
+changed in anyway.
+We need a method of pointing to some storage that can be altered
+and true to form, C provides a function called
+<a href=../FUNCTIONS/malloc.html>malloc</a> to do just that.
+<p>
+
+<hr>
+<h2>See Also:</h2>
+
+<img src=../../GRAPHICS/whiteball.gif>
+<a href=../SYNTAX/void.html>VOID keyword.</a>
+<hr>
+<p>
+<center>
+<table border=2 width=80% bgcolor=ivory>
+<tr align=center>
+<td width=25%>
+<a href=../cref.html>Top</a>
+</td><td width=25%>
+<a href=../master_index.html>Master Index</a>
+</td><td width=25%>
+<a href=../SYNTAX/keywords.html>Keywords</a>
+</td><td width=25%>
+<a href="../FUNCTIONS/funcref.htm">Functions</a>
+</td>
+</tr>
+</table>
+</center>
+<p>
+
+<hr>
+<address>Martin Leslie
+<script language="JavaScript">
+<!-- //
+document.write(document.lastModified);
+// -->
+</script>
+</address>
+
+