STRING(3) — C LIBRARY FUNCTIONS

NAME

string, strcat, strncat, strcmp, strncmp, strcpy, strncpy, strlen, strchr, strrchr, strpbrk, strspn, strcspn, strtok, index, rindex − string operations

SYNOPSIS

#include <string.h>

char ∗strcat (s1, s2)
char ∗s1, ∗s2;

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

int strcmp (s1, s2)
char ∗s1, ∗s2;

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

char ∗strcpy (s1, s2)
char ∗s1, ∗s2;

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

#include <string.h>

char ∗index(s, c)
char ∗s, c;

char ∗rindex(s, c)
char ∗s, c;

DESCRIPTION

These functions operate on null-terminated strings. They do not check for overflow of any receiving string.

strcat appends a copy of string s2 to the end of string s1. strncat appends at most n characters. Each returns a pointer to the null-terminated result.

strcmp compares its arguments and returns an integer greater than, equal to, or less than 0, according as s1 is lexicographically greater than, equal to, or less than s2. strncmp makes the same comparison but compares at most n characters.

strcpy copies string s2 to s1, stopping after the null character has been copied. strncpy copies exactly n characters, truncating or null-padding s2. 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.

index (rindex) 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. These functions are identical to strchr (strchr) and merely have different names.

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 pointer is returned.

NOTE

For user convenience, all these functions, except for index and rindex, are declared in the optional <string.h> header file. All these functions, including index and rindex but excluding strchr, strrchr, strpbrk, strspn, strcspn, and strtok, are declared in the optional <strings.h> include file; the reason for this is also historical.

WARNINGS

strcmp and strncmp use native character comparison, which is signed on the Sun, but may be unsigned on other machines. Thus the sign of the value returned when one of the characters has its high-order bit set is implementation-dependent.

On the Sun processor, as well as on many other machines, you can NOT use a NULL pointer to indicate a null string. A NULL pointer is an error and results in an abort of the program. If you wish to indicate a null string, you must have a pointer that points to an explicit null string. On some implementations of the C language on some machines, a NULL pointer, if dereferenced, would yield a null string; this highly non-portable trick was used in some programs. Programmers using a NULL pointer to represent an empty string should be aware of this portability issue; even on machines where dereferencing a NULL pointer does not cause an abort of the program, it does not necessarily yield a null string.

Character movement is performed differently in different implementations. Thus overlapping moves may yield surprises.