Built-in 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.