Library function in c

Some function in c language is built in within c library(Nothing but some collection). The library functions are built for sake of ready to use methodology.Function prototype and body are written within some header file in case of c programming language. Just programmer’s duty to call those library function by passing appropriate variable. Depending upon library function we need to include proper header file also.Some important library function of c programming language are

String Manipulation Functions

·         char *strcpy (char *dest, char *src);

Copy src string into dest string.

·         char *strncpy(char *string1, char *string2, int n);

Copy first n characters of string2 to stringl .

·         int strcmp(char *string1, char *string2);

Compare string1 and string2 to determine alphabetic order.

·         int strncmp(char *string1, char *string2, int n);

Compare first n characters of two strings.

·         int strlen(char *string);

Determine the length of a string.

·         char *strcat(char *dest, const char *src);

Concatenate string src to the string dest.

·         char *strncat(char *dest, const char *src, int n);

Concatenate n chracters from string src to the string dest.

·         char *strchr(char *string, int c);

Find first occurrence of character c in string.

·         char *strrchr(char *string, int c);

Find last occurrence of character c in string.

·         char *strstr(char *string2, char string*1);

Find first occurrence of string string1 in string2.

·         char *strtok(char *s, const char *delim) ;

Parse the string s into tokens using delim as delimiter.

Memory Management Functions

·         void *calloc(int num elems, int elem_size);

Allocate an array and initialise all elements to zero .

·         void free(void *mem address);

Free a block of memory.

·         void *malloc(int num bytes);

Allocate a block of memory.

·         void *realloc(void *mem address, int newsize);

Reallocate (adjust size) a block of memory.

Buffer Manipulation

·         void* memcpy(void* s, const void* ct, int n);

Copies n characters from ct to s and returns s. s may be corrupted if objects overlap.

·         int memcmp(const void* cs, const void* ct, int n);

Compares at most (the first) n characters of cs and ct, returning negative value if cs<ct, zero if cs==ct, positive value if cs>ct.

·         void* memchr(const void* cs, int c, int n);

Returns pointer to first occurrence of c in first n characters of cs, or NULL if not found.

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

Replaces each of the first n characters of s by c and returns s.

·         void* memmove(void* s, const void* ct, int n);

Copies n characters from ct to s and returns s. s will not be corrupted if objects overlap.

Character Functions

·         int isalnum(int c);

The function returns nonzero if c is alphanumeric

·         int isalpha(int c);

The function returns nonzero if c is alphabetic only

·         int iscntrl(int c);

The function returns nonzero if c is a control chracter

·         int isdigit(int c);

The function returns nonzero if c is a numeric digit

·         int isgraph(int c);

The function returns nonzero if c is any character for which either isalnum or ispunct returns nonzero.

·         int islower(int c);

The function returns nonzero if c is a lower case character.

·         int isprint(int c);

The function returns nonzero if c is space or a character for which isgraph returns nonzero.

·         int ispunct(int c);

The function returns nonzero if c is punctuation

·         int isspace(int c);

The function returns nonzero if c is space character

·         int isupper(int c);

The function returns nonzero if c is upper case character

·         int isxdigit(int c);

The function returns nonzero if c is hexa digit

·         int tolower(int c);

The function returns the corresponding lowercase letter if one exists and if isupper(c); otherwise, it returns c.

·         int toupper(int c);

The function returns the corresponding uppercase letter if one exists and if islower(c); otherwise, it returns c.

Error Handling Functions

·         void perror(const char *s);

produces a message on standard error output describing the last error encountered.

·         char *strerror(int errnum );

returns a string describing the error code passed in the argument errnum.

These are some library function that is in built in c library.The function may available depending upon compiler