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diff --git a/reference/C/CONCEPT/string.html b/reference/C/CONCEPT/string.html new file mode 100644 index 0000000..532f9d7 --- /dev/null +++ b/reference/C/CONCEPT/string.html @@ -0,0 +1,157 @@ +<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> + + |