From 7e0f021a9aec35fd8e6725e87e3313b101d26f5e Mon Sep 17 00:00:00 2001 From: Tobias Klauser Date: Sun, 27 Jan 2008 11:37:44 +0100 Subject: Initial import (2.0.2-6) --- reference/C/SYNTAX/null.html | 81 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) create mode 100644 reference/C/SYNTAX/null.html (limited to 'reference/C/SYNTAX/null.html') 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 @@ +Null + + + + +

NULL

+NULL is used in several ways. +

As a pointer to address zero. NULL is defined in several ANSI headers +as the +symbolic constant +(void *)0. 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. +
```
+	if ((fp=fopen("/etc/hosts","r") == NULL)
+        {
+          exit(0);
+        }
+
```
+
+
To mark the end of a character string. A null character is used to +terminate the string. For example if you coded: +
```
+	char * text="abc";
+
```
+You will actually reserve FOUR bytes containing in ASCII hex. +
```
+	61 62 63 00
+	 a  b  c \0
+
```
+The null at the end can be coded by using the +escape sequence '\0'. +

+\0 is actually an octal escape sequence, +strictly speeking it should +be written as \000 +

ANSI headers

+The following headers define NULL. +

locale.h +
stddef.h +
stdio.h +
stdlib.h +
string.h +
string.h +
time.h + + +
+ +
+
+
+ + + + +
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+ +
+
+
Martin Leslie +
+ + -- cgit v1.2.3-54-g00ecf