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# C - Built-in Library Functions

# 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.

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