String.h

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C Standard Library headers
C++ Standard Library headers
assert.h
complex.h
ctype.h
errno.h
fenv.h
float.h
inttypes.h
iso646.h
limits.h
locale.h
math.h
setjmp.h
signal.h
stdarg.h
stdbool.h
stddef.h
stdint.h
stdio.h
stdlib.h
string.h
tgmath.h
time.h
wchar.h
wctype.h

The correct title of this article is string.h. The initial letter is shown capitalized due to technical restrictions.

string.h is the header in the C standard library for the C programming language which contains macro definitions, constants, and declarations of functions and types used not only for string handling but also various memory handling functions; the name is thus something of a misnomer.

Functions declared in string.h are extremely popular, since as a part of the C standard library, they are guaranteed to work on any platform which supports C. However, some security issues exist with these functions, such as buffer overflows, leading programmers to prefer safer, possibly less portable variants. Also, the string functions only work with ASCII or character sets that extend ASCII in a compatible manner such as ISO-8859-1; multibyte ASCII-compatible character sets such as UTF-8 will work with the caveat that string "length" is to be interpreted as the count of bytes in the string rather than the count of Unicode characters. Non-ASCII compatible string handling is generally achieved through wchar.h.

1 Constants and types
2 Functions
- 2.1 Extensions to ISO C
3 External links

[edit] Constants and types

Name	Notes
`NULL`	a macro expanding to the null pointer constant; that is, a constant representing a pointer value which is guaranteed not to be a valid address of an object in memory.
`size_t`	an unsigned integer type which is the type of the result of the `sizeof` operator.

[edit] Functions

Name	Notes
`void memcpy(void dest, const void *src, size_t n);`	copies n bytes between two memory areas, which must not overlap
`void memmove(void dest, const void *src, size_t n);`	copies n bytes between two memory areas; unlike with `memcpy` the areas may overlap
`void memchr(const void s, int c, size_t n);`	returns a pointer to the first occurrence of c in the first n bytes of s, or NULL if not found
`int memcmp(const void s1, const void s2, size_t n);`	compares the first n characters of two memory areas
`void memset(void , int, size_t);`	overwrites a memory area with a byte pattern
`char strcat(char dest, const char *src);`	appends the string src to dest
`char strncat(char , const char *, size_t);`	appends at most n characters of the string src to dest
`char strchr(const char , int);`	locates a character in a string, searching from the beginning
`char strrchr(const char , int);`	locates a character in a string, searching from the end
`int strcmp(const char , const char );`	compares two strings numerically
`int strncmp(const char , const char , size_t);`	compares up to the first n bytes of two strings numerically
`int strcoll(const char , const char );`	compares two strings using the current locale's collating order
`char strcpy(char , const char *);`	copies a string from one location to another
`char strncpy(char , const char *, size_t);`	copies up to n bytes of a string from one location to another
`char *strerror(int);`	returns the string representation of errno (not thread-safe)
`size_t strlen(const char *);`	finds the length of a C string
`size_t strspn(const char s, const char accept);`	determines the length of the maximal initial substring of s consisting entirely of characters in accept
`size_t strcspn(const char s, const char reject);`	determines the length of the maximal initial substring of s consisting entirely of characters not in reject
`char strpbrk(const char s, const char *accept);`	finds the first occurrence of any character in accept in s
`char strstr(const char haystack, const char *needle);`	finds the first occurrence of needle in haystack
`char strtok(char , const char *);`	parses a string into a sequence of tokens; non-thread safe
`size_t strxfrm(char dest, const char src, size_t n);`	transforms src into a collating form, such that the numerical sort order of the transformed string is equivalent to the collating order of src.

[edit] Extensions to ISO C

Name	Notes	Specification
`char strdup(const char );`	allocates and duplicates a string into memory	POSIX; originally a BSD extension
`errno_t strcpy_s(char restrict s1, rsize_t s1max, const char restrict s2);`	bounds-checked variant of `strcpy`	ISO/IEC WDTR 24731
`void mempcpy(void dest, const void *src, size_t n);`	variant of `memcpy` returning a pointer to the byte following the last written byte	GNU
`void memccpy(void dest, const void *src, int c, size_t n` `);`	copies up to n bytes between two memory areas, which must not overlap, stopping when the byte c is found	UNIX 98?
`int strerror_r(int, char , size_t);`	returns the string representation of errno (thread-safe; some differences in semantics between GNU and XSI/POSIX)	GNU, POSIX
`size_t strlcpy(char dest, const char src, size_t n);`	bounds-checked variant of `strcpy`	originally OpenBSD, now also FreeBSD, Solaris, OS X
`char strtok_r(char , const char , char *);`	thread-safe version of strtok	POSIX