string.3c (2010 09)

s
string(3C) string(3C)
unsigned char. Null pointer values for s1 and s2 are treated the same as pointers to
empty strings.
strncmp() makes the same comparison but examines a maximum of n
characters (n less than or equal to zero yields equality).
strcasecmp() and
strncasecmp() are identical in function to strcmp() and
strncmp() respec-
tively, but characters are folded by
_tolower() (see conv(3C)) prior to comparison.
The returned lexicographic difference reflects the folding to lowercase.
strcpy() Copies string s2 to s1, stopping after the null byte has been copied.
strncpy() copies
exactly n characters, truncating s2 or adding null bytes to s1 if necessary, until a total of
n have been written. The result is not null-terminated if the length of s2 is n or more.
Each function returns s1. Note that
strncpy()
should not be used to copy n bytes of
an arbitrary structure. If that structure contains a null byte anywhere,
strncpy()
copies fewer than n bytes from the source to the destination and fills the remainder with
null bytes. Use the memcpy() function (see memory(3C)) to copy arbitrary binary data.
strdup() Returns a pointer to a new string which is a duplicate of the string to which s1 points.
The space for the new string is obtained using the
malloc() function (see malloc (3C)).
strlen() Returns the number of characters in s, not including the terminating null byte.
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 byte terminating a string is con-
sidered to be part of the string.
index() (rindex()) is identical to strchr()
(strrchr()), and is provided solely for portability of BSD applications.
strpbrk() Returns a pointer to the first occurrence in string s1 of any character from string s2,ora
null pointer if no character from s2 exists in s1.
strspn() (strcspn()) Returns the length of the maximum initial segment of string s1 , which
consists entirely of characters from (not from) string s2.
strstr() (strrstr()) Returns a pointer to the first (last) occurrence of string s2 in string s1,or
a NULL pointer if s2 does not occur in the string. If s2 points to a string of zero length,
strstr() (strrstr()) returns s1.
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 a non-
null pointer s1 specified) returns a pointer to the first character of the first token, and
writes a null byte into s1 immediately following the returned token. The function keeps
track of its position in the string s1 between separate calls, so that subsequent calls made
with the first argument a null pointer work through the string immediately following that
token. In this way subsequent calls work through the string s1 until no tokens remain.
The separator string s2 can be different from call to call. When no token remains in s1,a
null pointer is returned.
strtok_r() is identical to strtok(), except that it expects to be passed the address of a character
string pointer as the third argument. It will use this argument to keep track of the
current position in the string being searched. It returns a pointer to the current token in
the string or a NULL value if there are no more tokens.
strcoll() Returns an integer greater than, equal to, or less than zero, according to whether the
string pointed to by s1 is greater than, equal to, or less than the string pointed to by s2.
The comparison is based on strings interpreted as appropriate to the program’s locale (see
Locale below). In the ‘‘C’’ locale strcoll() works like strcmp().
strxfrm() Transforms the string pointed to by s2 and places the resulting string into the array
pointed to by s1. The transformation is such that if the strcmp() function is applied
to two transformed strings, it returns a value greater than, equal to, or less than zero,
corresponding to the result of the strcoll() function applied to the same two original
strings. No more than n bytes are placed into the resulting string, including the ter-
minating null character. If the transformed string fits in no more than n bytes, the
length of the resulting string is returned (not including the terminating null character).
Otherwise the return value is the number of bytes that the s1 string would occupy (not
including the terminating null character), and the contents of the array are indeter-
minate.
strcoll() has better performance with respect to strxfrm() in cases where a given string is com-
pared to other strings only a few times, or where the strings to be compared are long but a difference in
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