strcat, strncat, strcmp, strncmp, cistrcmp, cistrncmp, strcpy, strncpy, strecpy, strlen, strchr, strrchr, strpbrk, strspn, strcspn, strtok, strdup, strstr, cistrstr – string operations


#include <u.h>
#include <libc.h>

char* strcat(char *s1, char *s2)

char* strncat(char *s1, char *s2, long n)

int strcmp(char *s1, char *s2)

int strncmp(char *s1, char *s2, long n)

int cistrcmp(char *s1, char *s2)

int cistrncmp(char *s1, char *s2, long n)

char* strcpy(char *s1, char *s2)

char* strecpy(char *s1, char *es1, char *s2)

char* strncpy(char *s1, char *s2, long n)

long strlen(char *s)

char* strchr(char *s, int c)

char* strrchr(char *s, int c)

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

long strspn(char *s1, char *s2)

long strcspn(char *s1, char *s2)

char* strtok(char *s1, char *s2)

char* strdup(char *s)

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

char* cistrstr(char *s1, char *s2)


The arguments s1, s2 and s point to null-terminated strings. The functions strcat, strncat, strcpy, strecpy, and strncpy all alter s1. Strcat and strcpy 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. Strncat appends at most n bytes. 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 examines at most n bytes. Cistrcmp and cistrncmp ignore ASCII case distinctions when comparing strings. The comparisons are made with unsigned bytes.

Strcpy copies string s2 to s1, stopping after the null byte has been copied. Strncpy copies exactly n bytes, truncating s2 or adding null bytes to s1 if necessary. The result will not be null-terminated if the length of s2 is n or more. Each function returns s1.

Strecpy copies bytes until a null byte has been copied, but writes no bytes beyond es1. If any bytes are copied, s1 is terminated by a null byte, and a pointer to that byte is returned. Otherwise, the original s1 is returned.

Strlen returns the number of bytes in s, not including the terminating null byte.

Strchr (strrchr) returns a pointer to the first (last) occurrence of byte c in string s, or 0 if c does not occur in the string. The null byte terminating a string is considered to be part of the string.

Strpbrk returns a pointer to the first occurrence in string s1 of any byte from string s2, 0 if no byte from s2 exists in s1.

Strspn (strcspn) returns the length of the initial segment of string s1 which consists entirely of bytes 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 bytes from the separator string s2. The first call, with pointer s1 specified, returns a pointer to the first byte of the first token, and will have written a null byte into s1 immediately following the returned token. The function keeps track of its position in the string between separate calls; subsequent calls, signified by s1 being 0, will work through the string s1 immediately following that token. The separator string s2 may be different from call to call. When no token remains in s1, 0 is returned.

Strdup returns a pointer to a distinct copy of the null-terminated string s in space obtained from malloc(2) or 0 if no space can be obtained.

Strstr returns a pointer to the first occurrence of s2 as a substring of s1, or 0 if there is none. If s2 is the null string, strstr returns s1. Cistrstr operates analogously, but ignores ASCII case differences when comparing strings.


All these routines have portable C implementations in /sys/src/libc/port. Many also have machine-dependent assembly language implementations in /sys/src/libc/$objtype.


memory(2), rune(2), runestrcat(2), string(2)


These routines know nothing about UTF. Use the routines in rune(2) as appropriate. Note, however, that the definition of UTF guarantees that strcmp compares UTF strings correctly.

The outcome of overlapping moves varies among implementations.