Friday, January 27, 2012

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
Copy src string into dest string.
Copy first n characters of string2 to stringl .
Compare string1 and string2 to determine alphabetic order.
Compare first n characters of two strings.
·         int strlen(char *string);
Determine the length of a string.
Concatenate string src to the string dest.
Concatenate n chracters from string src to the string dest.
Find first occurrence of character c in string.
Find last occurrence of character c in string.
Find first occurrence of string string1 in string2.
Parse the string s into tokens using delim as delimiter.
Memory Management Functions
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.
Reallocate (adjust size) a block of memory.
Buffer Manipulation
Copies n characters from ct to s and returns s. s may be corrupted if objects overlap.
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.
Returns pointer to first occurrence of c in first n characters of cs, or NULL if not found.
Replaces each of the first n characters of s by c and returns s.
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
 



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