9.13 String Processing (<string.h>)

The <string.h> header file declares one type and several functions, and defines one macro useful for manipulating character arrays that other objects treat as character arrays.

There are two kinds of string functions declared. The first, with names beginning with str , manipulate character arrays; the second, with names beginning with mem , manipulate other objects treated as character arrays. Except for memmove , function behavior is undefined if copying takes place between overlapping objects.

Type

size_t


An unsigned integral type of the result of the sizeof operator.

Macro

NULL


Expands to an implementation-defined null pointer constant.

Functions

void *memcpy(void *s1, const void *s2, size_ t n);


Copies n characters from the object pointed to by s2 to the object pointed to by s1. The function returns s1.

void *memmove(void *s1, const void *s2, size_t n);


Copies n characters from the object pointed to by s2 to the object pointed to by s1. Copying takes place as if the n characters from the object pointed to by s2 are first copied into a temporary array of n characters that does not overlap the object pointed to by s1 and s2, and then the n characters from the temporary array are copied into the object pointed to by s1. The memmove function returns s1.

void *memchr(const void *s, int c, size_t n);


Locates the first occurrence of c (converted to an unsigned char ) in the first n unsigned characters of the object pointed to by s. The memchr function returns a pointer to the located character, or a null pointer if the character was not found.

int memcmp(const void *s1, const void *s2, size_t n);


Compares the first n characters of the object pointed to by s1 to the first n characters of the object pointed to by s2. The memcmp function returns an integer less than, equal to, or greater than 0, depending on whether the object pointed to by s1 is less than, equal to, or greater than the object pointed to by s2.

void *memset(void *s, int c, size_t n);


Copies the value of c (converted to an unsigned char) into each of the first n characters pointed to by s. The function returns s.

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


Copies the string pointed to by s2 (including the terminating null character) to the string pointed to by s1. The strcpy function returns s1.

char *strncpy(char *s1, const char *s2, size_t n);


Copies no more than n characters from the string pointed to by s2 to the string pointed to by s1, up to but not including the null terminator of the string pointed to by s2; returns s1. If the string pointed to by s2 is less than n characters, strncpy pads the copy with null characters.

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


Appends a copy of the the string pointed to by s2 (including the terminating null character) to the end of the string pointed to by s1. The strcat function returns s1. The first character of s2 overwrites the null character of s1.

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


Appends no more than n characters from the string pointed to by s2 (up to but not including a null character) to the string pointed to by s1. The strncat function returns s1. The first character of s2 overwrites the null character of s1. A terminating null character is appended to the result. The first character of s2 overwrites the null character of s1.

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


Compares the string pointed to by s1 to the string pointed to by s2. The strcmp function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2.

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


Compares the string pointed to by s1 to the string pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the current locale (see Section 9.5). The strcoll function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2, when both are interpreted as appropriate to the current locale.

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


Compares no more than n characters from the string pointed to by s1 to the string pointed to by s2. The strings are compared until a null character is encountered, the strings differ, or n is reached. The strncmp function returns an integer less than, equal to, or greater than 0, depending on whether the string pointed to by s1 is less than, equal to, or greater than the string pointed to by s2.

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


Transforms the string pointed to by s2 and places the resulting string into the array pointed to by s1.

See your DEC C library routine documentation for a detailed description of this function.

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


Locates the first occurrence of c (converted to a char ) in the string pointed to by s. The terminating null character is considered to be part of the string. The function returns a pointer to the located character, or a null pointer if the character was not found.

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


Computes the length of the maximum initial segment of the string pointed to by s1 that consists entirely of characters not found in the string pointed to by s2. The strcspn function returns the length of the segment.

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


Locates the first occurrence in the string pointed to by s1 of any character from the string pointed to by s2. The function returns a pointer to the character, or a null pointer if no character in s1 occurs in s2.

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


Locates the last occurrence of c (converted to a char ) in the string pointed to by s. The terminating null character is considered to be part of the string. The function returns a pointer to the located character, or a null pointer if the character was not found.

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


Computes the length of the maximum initial segment of the string pointed to by s1 that consists entirely of characters from the string pointed to by s2. The strspn function returns the length of the segment.

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


Locates the first occurrence in the string pointed to by s1 of the sequence of characters (excluding the terminal null character) in the string pointed to by s2. The strstr function returns a pointer to the located string, or a null pointer if the string was not found. If s2 points to a string of zero length, the function returns s1.

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


Breaks the string pointed to by s1 into a sequence of tokens, each of which is delimited by a character from the string pointed to by s2. The first call to strtok () skips characters, looking for the first one that is not in s2. The function keeps track of its position in the string pointed to by s1 between calls and, as successive calls are made, the function works through this string, identifying the text token following the one identified by the previous call. When the function finds a character in s1 that matches a character in s2, it replaces the character in s1 with a null character. The strtok function returns a pointer to the first character of the token, or a null pointer if there is no token.

char *strerror(int errnum);


Maps the error number in errnum to an error message string; returns a pointer to the string. The string pointed to must not be modified by the program, but can be overwritten by a subsequent call to strerror .

size_t strlen(const char *s);


Computes the length of the string pointed to by s. The function returns the number of characters that precede the terminating null character.


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