NAME

string: strcat, strdup, strncat, strcmp, strncmp, strcasecmp, strncasecmp, strcpy, strncpy, strlen, strchr, strrchr, strpbrk, strspn, strcspn, strtok − string operations

SYNOPSIS

#include <string.h>
#include <sys/types.h>

char ∗strcat (s1, s2)
char ∗s1, ∗s2;

char ∗strdup (s1)
char ∗s1;

char ∗strncat (s1, s2, n)
char ∗s1, ∗s2;
size_t n;

int strcmp (s1, s2)
char ∗s1, ∗s2;

int strncmp (s1, s2, n)
char ∗s1, ∗s2;
size_t n;

strcasecmp(s1, s2)
char ∗s1, ∗s2;

strncasecmp(s1, s2, count)
char ∗s1, ∗s2;
int count;

char ∗strcpy (s1, s2)
char ∗s1, ∗s2;

char ∗strncpy (s1, s2, n)
char ∗s1, ∗s2;
size_t n;

int strlen (s)
char ∗s;

char ∗strchr (s, c)
char ∗s;
int c;

char ∗strrchr (s, c)
char ∗s;
int c;

char ∗strpbrk (s1, s2)
char ∗s1, ∗s2;

int strspn (s1, s2)
char ∗s1, ∗s2;

int strcspn (s1, s2)
char ∗s1, ∗s2;

char ∗strtok (s1, s2)
char ∗s1, ∗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.  strcasecmp and strncasecmp are identical in function, but are case insensitive.  The returned lexicographic difference reflects a conversion to lower-case. 

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 is not 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. 

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) works through the string s1 immediately following that token.  In this way subsequent calls 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 pointer is returned. 

For user convenience, all these functions are declared in the optional <string.h> header file. 

SEE ALSO

malloc(3C), malloc(3X)

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 is 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. 

September 29, 2021