diff options
| author | Tobias Klauser <tklauser@distanz.ch> | 2008-01-27 11:37:44 +0100 |
|---|---|---|
| committer | Tobias Klauser <tklauser@xenon.tklauser.home> | 2008-01-27 11:37:44 +0100 |
| commit | 7e0f021a9aec35fd8e6725e87e3313b101d26f5e (patch) | |
| tree | b1cacc4b24393f517aeb4610e9e1021f954307a8 /reference/C/SYNTAX/null.html | |
Initial import (2.0.2-6)2.0.2-6
Diffstat (limited to 'reference/C/SYNTAX/null.html')
| -rw-r--r-- | reference/C/SYNTAX/null.html | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/reference/C/SYNTAX/null.html b/reference/C/SYNTAX/null.html new file mode 100644 index 0000000..143b52a --- /dev/null +++ b/reference/C/SYNTAX/null.html @@ -0,0 +1,81 @@ +<title>Null</title> +<head> +<script language="JavaScript"> +</script> +</head> +<body bgcolor="#ffffcc"> +<hr> +<center><h1>NULL</h1></center> +<hr> +<p> +NULL is used in several ways. +<ul> +<li>As a pointer to address zero. NULL is defined in several ANSI headers +as the +<a href="define_preprocessor.html">symbolic constant</a> +<a href="../CONCEPT/pointers.html#void">(void *)0</a>. Zero is often returned from +functions that normaly return a pointer to signal an error. It is therefore +conveniant to compare a function return code with NULL to catch errors. +<pre> + if ((fp=<a href="../FUNCTIONS/fopen.html">fopen</a>("/etc/hosts","r") == NULL) + { + exit(0); + } +</pre> +<p> +<li>To mark the end of a character string. A null character is used to +terminate the string. For example if you coded: +<pre> + char * text="abc"; +</pre> +You will actually reserve <b>FOUR</b> bytes containing in ASCII hex. +<pre> + 61 62 63 00 + a b c \0 +</pre> +The null at the end can be coded by using the +<a href="../FUNCTIONS/escape.html">escape sequence</a> '\0'. +</ul> +<p> +\0 is actually an octal <a href="../FUNCTIONS/escape.html">escape sequence</a>, +strictly speeking it should +be written as \000 +<p> +<hr> +<h2>ANSI headers</h2> +The following headers define NULL. +<ul> +<li><a href="../FUNCTIONS/funcref.htm#headers">locale.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">stddef.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">stdio.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">stdlib.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">string.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">string.h</a> +<li><a href="../FUNCTIONS/funcref.htm#headers">time.h</a> + + +<p> + +<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="keywords.html"> Keywords</a> +</td><td width="25%"> +<a href="../FUNCTIONS/funcref.htm"> Functions</a> +</td> +</tr> +</table> +</center> +<p> +<hr> +<address>Martin Leslie +</address><p> +</body> +</html> |