string(3C)

NAME

string: strcasecmp(), strcat(), strchr(), strcmp(), strcoll(), strcpy(), strcspn(), strdup(), strlen(), strncasecmp(), strncat(), strncmp(), strncpy(), strpbrk(), strrchr(), strrstr(), strspn(), strstr(), strtok(), strtok_r(), strxfrm(), index(), rindex() — character string operations

SYNOPSIS

#include <string.h> 
#include <strings.h> 

char *strcat(char *__restrict s1, const char *__restrict s2); 

char *strncat(char *__restrict s1, const char *__restrict s2, size_t n); 

int strcmp(const char *s1, const char *s2); 

int strncmp(const char *s1, const char *s2, size_t n); 

int strcasecmp(const char *s1, const char *s2); 

int strncasecmp(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); 

char *strdup(const char *s); 

size_t strlen(const char *s); 

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

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

char *strpbrk(const char *s1, const char *s2); 

size_t strspn(const char *s1, const char *s2); 

size_t strcspn(const char *s1, const char *s2); 

char *strstr(const char *s1, const char *s2); 

char *strrstr(const char *s1, const char *s2); 

char *strtok(char *__restrict s1, const char *__restrict s2); 

char *strtok_r(char *s1, const char *s2, char **last); 

int strcoll(const char *s1, const char *s2); 

size_t strxfrm(char *__restrict s1, const char *__restrict s2, size_t n); 

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

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

Remarks

All functions except index() and rindex() are declared in both headers, so only one of the two headers needs to be included.

The functions index() and rindex() are declared only in <strings.h>. They are provided solely for portability of BSD applications, and are not recommended for new applications where portability is important. For portable applications, use <string.h>, strchr(), and strrchr() instead.

DESCRIPTION

Arguments s1, s2, and s point to strings (arrays of characters terminated by a null byte).

Definitions for all these functions, the type size_t, and the constant NULL are provided in the <string.h> header.

strcat(): Appends a copy of string s2 to the end of string s1. strncat() appends a maximum of n characters. It copies fewer if s2 is shorter than n characters. Each returns a pointer to the null-terminated result (the value of s1).
strcmp(): Compares its arguments and returns an integer less than, equal to, or greater than zero, depending on whether s1 is lexicographically less than, equal to, or greater than s2. The comparison of corresponding characters is done as if the type of the characters were 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() respectively, 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 considered 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, or a 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 nonnull 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 terminating 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 indeterminate.

strcoll() has better performance with respect to strxfrm() in cases where a given string is compared to other strings only a few times, or where the strings to be compared are long but a difference in the strings that determines their relative ordering usually comes among the first few characters. strxfrm() offers better performance in, for example, a sorting routine where a number of strings are each transformed just once and the transformed versions are compared against each other many times.

EXTERNAL INFLUENCES

Locale

The LC_CTYPE category determines the interpretation of the bytes within the string arguments to the strcoll() and strxfrm() functions as single and/or multibyte characters. It also determines the case conversions to be done for the strcasecmp() and strncasecmp() functions.

The LC_COLLATE category determines the collation ordering used by the strcoll() and strxfrm() functions.

International Code Set Support

Single- and multibyte character code sets are supported for the strcoll() and strxfrm() functions. All other functions support only single-byte character code sets.

EXAMPLES

The following sample piece of code finds the tokens, separated by blanks, that are in the string s (assuming that there are at most MAXTOK tokens):

int i = 0;
char *s, *last, *tok[MAXTOK];

tok[0] = strtok_r(s, " ", &last);
while (tok[++i] = strtok_r(NULL, " ", &last));

WARNINGS

The functions strcat(), strncat(), strcpy(), strncpy(), strtok(), and strtok_r() alter the contents of the array to which s1 points. They do not check for overflow of the array.

Null pointers for destination strings cause undefined behavior.

Character movement is performed differently in different implementations, so moves involving overlapping source and destination strings may yield surprises.

The transformed string produced by strxfrm() for a language using an 8-bit code set is usually at least twice as large as the original string and may be as much four times as large (ordinary characters occupy two bytes each in the transformed string, 1-to-2 characters four bytes, 2-to-1 characters two bytes per original pair, and don't-care characters no bytes). Each character of a multibyte code set (Asian languages) occupies three bytes in the transformed string.

For functions strcoll() and strxfrm() results are undefined if the languages specified by the LC_COLLATE and LC_CTYPE categories use different code sets.

Users of strtok_r() should also note that the prototype of this function will change in the next release for conformance with the new POSIX Threads standard.

AUTHOR

string() was developed by the University of California, Berkeley, AT&T, OSF, and HP.

STANDARDS CONFORMANCE

strcat(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strchr(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strcmp(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strcoll(): AES, SVID3, XPG3, XPG4, ANSI C

strcpy(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strcspn(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strdup(): SVID2, SVID3

strlen(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strncat(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strncmp(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strncpy(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strpbrk(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strrchr(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strspn(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strstr(): AES, SVID3, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strtok(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

strxfrm(): AES, SVID3, XPG3, XPG4, ANSI C