C programming/string.h

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 characters encodings made of bytes, such as ASCII and UTF-8. In historical documentation the term "character" was often used instead of "byte", which if followed literally would mean that multi-byte encodings such as UTF-8 were not supported. The BSD documentation has been fixed to make this clear, but POSIX, Linux, and Windows documentation still uses "character" in many places. Functions to handle character encodings made up of larger code units than bytes, such as UTF-16 is generally achieved through wchar.h. Constants and types Name NotesNULL 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. Functions Name Notesvoid *memcpy(void *dest, const void *src, size_t n);copies n bytes between two memory areas; if there is overlap, the behavior is undefinedvoid *memmove(void *dest, const void *src, size_t n);copies n bytes between two memory areas; unlike with memcpy the areas may overlapvoid *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 foundint memcmp(const void *s1, const void *s2, size_t n);compares the first n bytes of two memory areasvoid *memset(void *, int c, size_t n);overwrites a memory area with n copies of cchar *strcat(char *dest, const char *src);appends the string src to destchar *strncat(char *dest, const char *src, size_t n);appends at most n bytes of the string src to destchar *strchr(const char *, int c);locates byte c in a string, searching from the beginningchar *strrchr(const char *, int c);locates byte c in a string, searching from the endint strcmp(const char *, const char *);compares two strings lexicographicallyint strncmp(const char *, const char *, size_t n);compares up to the first n bytes of two strings lexicographicallyint strcoll(const char *, const char *);compares two strings using the current locale's collating orderchar *strcpy(char *dest, const char *src);copies a string from one location to anotherchar *strncpy(char *dest, const char *src, size_t n);write exactly n bytes to dest, copying from src or add 0'schar *strerror(int);returns the string representation of an error number e.g. errno (not thread-safe)size_t strlen(const char *);finds the length of a C stringsize_t strspn(const char *, const char *accept);determines the length of the maximal initial substring consisting entirely of bytes in acceptsize_t strcspn(const char *, const char *reject);determines the length of the maximal initial substring consisting entirely of bytes not in rejectchar *strpbrk(const char *, const char *accept);finds the first occurrence of any byte in acceptchar *strstr(const char *haystack, const char *needle);finds the first occurrence of the string "needle" in the longer string "haystack"char *strtok(char *, const char * delim);parses a string into a sequence of tokens; non-thread safe in the spec, non-reentranthttp://pubs.opengroup.org/onlinepubs/009695399/functions/strtok.htmlsize_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 Extensions to ISO C Name Notes Specificationvoid *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 foundSVID, POSIXhttp://pubs.opengroup.org/onlinepubs/009695399/functions/memccpy.htmlvoid *mempcpy(void *dest, const void *src, size_t n); mempcpy() is a variant of memcpy returning a pointer to the byte following the last written byteGNUerrno_t strcat_s(char *dest, size_t n, const char *src);bounds-checked variant of strcatISO/IEC WDTR 24731errno_t strcpy_s(char *dest, size_t n, const char *src);bounds-checked variant of strcpyISO/IEC WDTR 24731char *strdup(const char *src);allocates and duplicates a string into memoryPOSIX; originally a BSD extensionint strerror_r(int, char *, size_t);Puts the result of strerror() into the provided buffer in a thread-safe way.POSIX:2001char *strerror_r(int, char *, size_t);Return strerror() in a thread-safe way. The provided buffer is used only if necessary (incompatible with POSIX version).GNUsize_t strlcat(char *dest, const char *src, size_t n);bounds-checked variant of strcatoriginally OpenBSD, now also FreeBSD, Solaris, Mac OS Xsize_t strlcpy(char *dest, const char *src, size_t n);bounds-checked variant of strcpyoriginally OpenBSD, now also FreeBSD, Solaris, Mac OS Xchar *strsignal(int sig);by analogy to strerror, returns string representation of the signal sig (not thread safe)POSIX:2008http://pubs.opengroup.org/onlinepubs/9699919799/functions/strsignal.htmlchar *strtok_r(char *, const char *delim, char **saveptr);thread-safe and reentrant version of strtokPOSIX References External links 3 string string operations C++ reference for string functions inherited from C