string(3C) string(3C)
NAME
string, strcasecmp, strncasecmp, strcat, strncat, strlcat, strchr, strrchr, strcmp, strncmp, strcpy, strncpy, strlcpy, strcspn, strspn,
strdup, strlen, strpbrk, strstr, strtok, strtok_r - string operations
SYNOPSIS
#include <strings.h>
int strcasecmp(const char *s1, const char *s2);
int strncasecmp(const char *s1, const char *s2, size_t n);
#include <string.h>
char *strcat(char *restrict s1, const char *restrict s2);
char *strncat(char *restrict s1, const char *restrict s2, size_t n);
size_t strlcat(char *dst, const char *src, size_t dstsize);
char *strchr(const char *s, int c);
char *strrchr(const char *s, int c);
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);
char *strcpy(char *restrict s1, const char *restrict s2);
char *strncpy(char *restrict s1, const char *restrict s2, size_t n);
size_t strlcpy(char *dst, const char *src, size_t dstsize);
size_t strcspn(const char *s1, const char *s2);
size_t strspn(const char *s1, const char *s2);
char *strdup(const char *s1);
size_t strlen(const char *s);
char *strpbrk(const char *s1, const char *s2);
char *strstr(const char *s1, const char *s2);
char *strtok(char *restrict s1, const char *restrict s2);
char *strtok_r(char *s1, const char *s2, char **lasts);
ISO C++
#include <string.h>
const char *strchr(const char *s, int c);
const char *strpbrk(const char *s1, const char *s2);
const char *strrchr(const char *s, int c);
const char *strstr(const char *s1, const char *s2);
#include <cstring>
char *std::strchr(char *s, int c);
char *std::strpbrk(char *s1, const char *s2);
char *std::strrchr(char *s, int c);
char *std::strstr(char *s1, const char *s2);
The arguments s, s1, and s2 point to strings (arrays of characters terminated by a null character). The strcat(), strncat(), strlcat(),
strcpy(), strncpy(), strlcpy(), strtok(), and strtok_r() functions all alter their first argument. These functions do not check for over-
flow of the array pointed to by the first argument.
strcasecmp(), strncasecmp()
The strcasecmp() and strncasecmp() functions are case-insensitive versions of strcmp() and strncmp() respectively, described below. They
assume the ASCII character set and ignore differences in case when comparing lower and upper case characters.
strcat(), strncat(), strlcat()
The strcat() function appends a copy of string s2, including the terminating null character, to the end of string s1. The strncat() func-
tion appends at most n characters. Each returns a pointer to the null-terminated result. The initial character of s2 overrides the null
character at the end of s1.
The strlcat() function appends at most (dstsize-strlen(dst)-1) characters of src to dst (dstsize being the size of the string buffer
dst). If the string pointed to by dst contains a null-terminated string that fits into dstsize bytes when strlcat() is called, the string
pointed to by dst will be a null-terminated string that fits in dstsize bytes (including the terminating null character) when it completes,
and the initial character of src will override the null character at the end of dst. If the string pointed to by dst is longer than dst-
size bytes when strlcat() is called, the string pointed to by dst will not be changed. The function returns min{dst-
size,strlen(dst)}+strlen(src). Buffer overflow can be checked as follows:
if (strlcat(dst, src, dstsize) >= dstsize)
return -1;
strchr(), strrchr()
The strchr() function returns a pointer to the first occurrence of c (converted to a char) in string s, or a null pointer if c does not
occur in the string. The strrchr() function returns a pointer to the last occurrence of c. The null character terminating a string is con-
sidered to be part of the string.
strcmp(), strncmp()
The strcmp() function compares two strings byte-by-byte, according to the ordering of your machine's character set. The function returns
an integer greater than, equal to, or less than 0, if the string pointed to by s1 is greater than, equal to, or less than the string
pointed to by s2 respectively. The sign of a non-zero return value is determined by the sign of the difference between the values of the
first pair of bytes that differ in the strings being compared. The strncmp() function makes the same comparison but looks at a maximum of n
bytes. Bytes following a null byte are not compared.
strcpy(), strncpy(), strlcpy()
The strcpy() function copies string s2 to s1, including the terminating null character, stopping after the null character has been copied.
The strncpy() function copies exactly n bytes, truncating s2 or adding null characters to s1 if necessary. The result will not be null-ter-
minated if the length of s2 is n or more. Each function returns s1.
The strlcpy() function copies at most dstsize-1 characters (dstsize being the size of the string buffer dst) from src to dst, truncat-
ing src if necessary. The result is always null-terminated. The function returns strlen(src). Buffer overflow can be checked as follows:
if (strlcpy(dst, src, dstsize) >= dstsize)
return -1;
strcspn(), strspn()
The strcspn() function returns the length of the initial segment of string s1 that consists entirely of characters not from string s2. The
strspn() function returns the length of the initial segment of string s1 that consists entirely of characters from string s2.
strdup()
The strdup() function returns a pointer to a new string that is a duplicate of the string pointed to by s1. The returned pointer can be
passed to free(). The space for the new string is obtained using malloc(3C). If the new string cannot be created, a null pointer is
returned and errno may be set to ENOMEM to indicate that the storage space available is insufficient.
strlen()
The strlen() function returns the number of bytes in s, not including the terminating null character.
strpbrk()
The strpbrk() function 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.
strstr()
The strstr() function locates the first occurrence of the string s2 (excluding the terminating null character) in string s1 and 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 (that is, the
string ""), the function returns s1.
strtok()
A sequence of calls to strtok() breaks the string pointed to by s1 into a sequence of tokens, each of which is delimited by a byte from the
string pointed to by s2. The first call in the sequence has s1 as its first argument, and is followed by calls with a null pointer as their
first argument. The separator string pointed to by s2 can be different from call to call.
The first call in the sequence searches the string pointed to by s1 for the first byte that is not contained in the current separator
string pointed to by s2. If no such byte is found, then there are no tokens in the string pointed to by s1 and strtok() returns a null
pointer. If such a byte is found, it is the start of the first token.
The strtok() function then searches from there for a byte that is contained in the current separator string. If no such byte is found, the
current token extends to the end of the string pointed to by s1, and subsequent searches for a token return a null pointer. If such a byte
is found, it is overwritten by a null byte that terminates the current token. The strtok() function saves a pointer to the following byte
in thread-specific data, from which the next search for a token starts.
Each subsequent call, with a null pointer as the value of the first argument, starts searching from the saved pointer and behaves as
described above.
See Example 1, 2, and 3 in the section for examples of strtok() usage.
strtok_r()
The strtok_r() function considers the null-terminated string s1 as a sequence of zero or more text tokens separated by spans of one or more
characters from the separator string s2. The argument lasts points to a user-provided pointer which points to stored information necessary
for strtok_r() to continue scanning the same string.
In the first call to strtok_r(), s1 points to a null-terminated string, s2 to a null-terminated string of separator characters, and the
value pointed to by lasts is ignored. The strtok_r() function returns a pointer to the first character of the first token, writes a null
character into s1 immediately following the returned token, and updates the pointer to which lasts points.
In subsequent calls, s1 is a null pointer and lasts is unchanged from the previous call so that subsequent calls move through the string
s1, returning successive tokens until no tokens remain. The separator string s2 can be different from call to call. When no token remains
in s, a null pointer is returned.
See Example 3 in the section for an example of strtok_r() usage.
Example 1: Search for word separators.
The following example searches for tokens separated by space characters.
#include <string.h>
...
char *token;
char *line = "LINE TO BE SEPARATED";
char *search = " ";
/* Token will point to "LINE". */
token = strtok(line, search);
/* Token will point to "TO". */
token = strtok(NULL, search);
Example 2: Break a Line.
The following example uses strtok to break a line into two character strings separated by any combination of SPACEs, TABs, or NEWLINEs.
#include <string.h>
...
struct element {
char *key;
char *data;
};
...
char line[LINE_MAX];
char *key, *data;
...
key = strtok(line, "
");
data = strtok(NULL, "
");
Example 3: Search for tokens.
The following example uses both strtok() and strtok_r() to search for tokens separated by one or more characters from the string pointed to
by the second argument, "/".
#define __EXTENSIONS__
#include <stdio.h>
#include <string.h>
int
main() {
char *buf="5/90/45";
char *token;
char *lasts;
printf("tokenizing "%s" with strtok():
", buf);
if ((token = strtok(buf, "/")) != NULL) {
printf("token = "%s"
", token);
while ((token = strtok(NULL, "/")) != NULL) {
printf("token = "%s"
", token);
}
}
buf = "//5//90//45//";
printf("
tokenizing "%s" with strtok_r():
", buf);
if ((token = strtok_r(buf, "/", &lasts)) != NULL) {
printf("token = "%s"
", token);
while ((token = strtok_r(NULL, "/", &lasts)) != NULL) {
printf("token = "%s"
", token);
}
}
}
When compiled and run, this example produces the following output:
tokenizing "5/90/45" with strtok():
token = "5"
token = "90"
token = "45"
tokenizing "//5//90//45//" with strtok_r():
token = "5"
token = "90"
token = "45"
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |See below. |
+-----------------------------+-----------------------------+
|MT-Level |See below. |
+-----------------------------+-----------------------------+
The strlcat() and strlcpy() functions are Stable. The remaining functions are Standard.
The strtok() and strdup() functions are MT-Safe. The remaining functions are Async-Signal-Safe.
malloc(3C), setlocale(3C), strxfrm(3C), attributes(5), standards(5)
When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should only be used in multi-
threaded applications.
A single-threaded application can gain access to strtok_r() only by defining __EXTENSIONS__ or by defining _POSIX_C_SOURCE to a value
greater than or equal to 199506L.
All of these functions assume the default locale ``C.'' For some locales, strxfrm(3C) should be applied to the strings before they are
passed to the functions.
The strtok() function is safe to use in multithreaded applications because it saves its internal state in a thread-specific data area.
However, its use is discouraged, even for single-threaded applications. The strtok_r() function should be used instead.
17 Feb 2004 string(3C)