int strcmp(char *s1, char *s2)

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

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

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

long strlen(char *s)

char* strchr(char *s, char c)

char* strrchr(char *s, char c)

char* strdup(char *s)

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

Strcat appends a copy of string s2 to the end of string s1, and 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. 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.

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.

Strdup returns a pointer to a distinct copy of the null-terminated string s in space obtained from malloc(10.2) 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.

The outcome of overlapping moves varies among implementations.

Note the absence of ANSI C's strncat, strpbrk, strspn, strcspn and strtok, but the presence of strdup.