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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%>
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</td><td width=25%>
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</center>
<p>
<hr>
<address>Martin Leslie
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