STRING(3C) SysV STRING(3C)
NAME
string: strcat, strdup, strncat, strcmp, strncmp, strxfrm, strcoll,
strcpy, strncpy, strlen, strchr, strrchr, strstr, strpbrk, strspn,
strcspn, strtok - string operations
SYNOPSIS
#include <string.h>
#include <sys/types.h>
char *strcat (s1, s2)
char *s1;
const char *s2;
char *strdup (s1)
char *s1;
char *strncat (s1, s2, n)
char *s1;
const char *s2;
size_t n;
int strcmp (s1, s2)
const char *s1, *s2;
int strncmp (s1, s2, n)
const char *s1, *s2;
size_t n;
size_t strxfrm(s1, s2, n)
char *s1;
const char*s2;
size_t n;
int strcoll(s1, s2)
const char *s1, *s2;
char *strcpy (s1, s2)
char *s1;
const char *s2;
char *strncpy (s1, s2, n)
char *s1;
const char *s2;
size_t n;
size_t strlen (s)
const char *s;
char *strchr (s, c)
const char *s;
int c;
char *strrchr (s, c)
const char *s;
int c;
char *strstr(s1, s2)
const char *s1, *s2;
char *strpbrk (s1, s2)
const char *s1, *s2;
size_t strspn (s1, s2)
const char *s1, *s2;
size_t strcspn (s1, s2)
const char *s1, *s2;
char *strtok (s1, s2)
char *s1;
const char *s2;
DESCRIPTION
The arguments s1, s2 and s point to strings (arrays of characters
terminated by a null character). The functions strcat, strncat, strcpy,
and strncpy all alter s1. These functions do not check for overflow of
the array pointed to by s1.
strcat appends a copy of string s2 to the end of string s1.
strdup returns a pointer to a new string which is a duplicate of the
string pointed to by s1. The space for the new string is obtained using
malloc(3C). If the new string can not be created, null is returned.
strncat appends at most n characters. Each returns a pointer to the null
terminated result.
strcmp compares its arguments and returns an integer less than, equal to,
or greater than 0, according as s1 is lexicographically less than, equal
to, or greater than s2. strncmp makes the same comparison but looks at
at most n characters.
strxfrm transforms s2 and places it into s1. The transformation is such
that if strcmp is applied to two transformed strings, it returns a value
greater than, equal to, or less than zero, corresponding to the result of
strcoll applied to the same two original strings. No more than n
characters are placed into s1, including the terminating null character.
If n is zero, s1 is can be a null pointer. If copying takes place
between objects that overlap, the behavior is undefined. strxfrm returns
the length of the transformed string (not including the terminating null
character). If the value returned is n or more, the contents of s1 are
indeterminate.
strcoll compares string s1 to string s2, both interpreted as appropriate
to the LC_COLLATE category of the current locale. It returns an integer
greater than, equal to, or less than zero, according as s1 is greater
than, equal to, or less than s2 when both are interpreted as appropriate
to the current locale.
strcpy copies string s2 to s1, stopping after the null character has been
copied. strncpy copies exactly n characters, truncating s2 or adding
null characters to s1 if necessary. The result will not be null
terminated if the length of s2 is n or more. Each function returns s1.
strlen returns the number of characters in s, not including the
terminating null character.
strchr (strrchr) returns a pointer to the first (last) occurrence of
character c in string s, or 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.
strstr locates the first occurrence in s1 of the sequence of characters
(excluding the terminating null character) in s2. It returns a pointer
to the located string, or a null pointer if the string is not found. If
s2 points to a string with zero length, strstr returns s1.
strpbrk returns a pointer to the first occurrence in string s1 of any
character from string s2, or a NULL pointer if no character from s2
exists in s1.
strspn (strcspn) returns the length of the initial segment of string s1
which consists entirely of characters from (not from) string s2.
strtok considers the string s1 to consist of a sequence of zero or more
text tokens separated by spans of one or more characters from the
separator string s2. The first call (with pointer s1 specified) returns
a pointer to the first character of the first token, and will have
written a null character into s1 immediately following the returned
token. The function keeps track of its position in the string between
separate calls, so that subsequent calls (which must be made with the
first argument a NULL pointer) will work through the string s1
immediately following that token. In this way subsequent calls will work
through the string s1 until no tokens remain. The separator string s2
may be different from call to call. When no token remains in s1, a NULL
is returned.
EXAMPLES
The following expression evaluates to the size of the array needed to
hold the transformation of the string pointed to by s:
1 + strxfrm(NULL, s, 0)
The following extracts tokens from a string using successive calls to
strtok.
#include <string.h>
static char str[] = "?a???b,,,#c";
char *t;
t = strtok(str, "?"); /* t points to the token "a" */
t = strtok(NULL, ","); /* t points to the token "??b" */
t = strtok(NULL, "#,"); /* t points to the token "c" */
t = strtok(NULL, "?"); /* t is a null pointer */
SEE ALSO
intro(3), malloc(3C), malloc(3X).
NOTES
You may obtain in-line versions of strcpy, strncpy, strncat, strcat,
strcmp, strncmp, and strlen by adding the directive
#define _STRING_BUILTINS
or the directive
#define _BUILTINS
before any #include directives in your program. If you use the
#define _BUILTINS
directive, _MATH_BUILTINS gets defined, too. See intro(3).
Parts of this discussion are adapted from ANS X3.159-1989.
CAVEATS
strcmp and strncmp are implemented by using the most natural character
comparison on the machine. Thus the sign of the value returned when one
of the characters has its high-order bit set not the same in all
implementations and should not be relied upon.
Character movement is performed differently in different implementations.
Thus overlapping moves may yield surprises.