INDEX(3C) Standard C Library Functions INDEX(3C)


index, rindex - string operations


#include <strings.h>

char *index(const char *s, int c);

char *rindex(const char *s, int c);


The index() and rindex() functions operate on null-terminated strings.

The index() function returns a pointer to the first occurrence of
character c in string s.

The rindex() function returns a pointer to the last occurrence of
character c in string s.

Both index() and rindex() return a null pointer if c does not occur in
the string. The null character terminating a string is considered to be
part of the string.


On most modern computer systems, you can not use a null pointer to
indicate a null string. A null pointer is an error and results in an
abort of the program. If you wish to indicate a null string, you must
use a pointer that points to an explicit null string. On some machines
and with some implementations of the C programming language, a null
pointer, if dereferenced, would yield a null string. Though often used,
this practice is not always portable. Programmers using a null pointer to
represent an empty string should be aware of this portability issue.
Even on machines where dereferencing a null pointer does not cause an
abort of the program, it does not necessarily yield a null string.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |


bstring(3C), malloc(3C), string(3C), attributes(7), standards(7)

July 24, 2002 INDEX(3C)