C Library - < string. h >

The string.h header defines one variable type, one macro, and various functions for manipulating arrays of characters.

Library Variables

Following is the variable type defined in the header string.h −

Sr.No.	Variable & Description
1	size_t This is the unsigned integral type and is the result of the sizeof keyword.

Library Macros

Following is the macro defined in the header string.h −

Sr.No.	Macro & Description
1	NULL This macro is the value of a null pointer constant.

Library Functions

Following are the functions defined in the header string.h −

Sr.No.	Function & Description
1	void *memchr(const void *str, int c, size_t n) Searches for the first occurrence of the character c (an unsigned char) in the first n bytes of the string pointed to, by the argument str.
2	int memcmp(const void *str1, const void *str2, size_t n) Compares the first n bytes of str1 and str2.
3	void *memcpy(void *dest, const void *src, size_t n) Copies n characters from src to dest.
4	void *memmove(void *dest, const void *src, size_t n) Another function to copy n characters from str2 to str1.
5	void *memset(void *str, int c, size_t n) Copies the character c (an unsigned char) to the first n characters of the string pointed to, by the argument str.
6	char *strcat(char *dest, const char *src) Appends the string pointed to, by src to the end of the string pointed to by dest.
7	char *strncat(char *dest, const char *src, size_t n) Appends the string pointed to, by src to the end of the string pointed to, by dest up to n characters long.
8	char *strchr(const char *str, int c) Searches for the first occurrence of the character c (an unsigned char) in the string pointed to, by the argument str.
9	int strcmp(const char *str1, const char *str2) Compares the string pointed to, by str1 to the string pointed to by str2.
10	int strncmp(const char *str1, const char *str2, size_t n) Compares at most the first n bytes of str1 and str2.
11	int strcoll(const char *str1, const char *str2) Compares string str1 to str2. The result is dependent on the LC_COLLATE setting of the location.
12	char *strcpy(char *dest, const char *src) Copies the string pointed to, by src to dest.
13	char *strncpy(char *dest, const char *src, size_t n) Copies up to n characters from the string pointed to, by src to dest.
14	size_t strcspn(const char *str1, const char *str2) Calculates the length of the initial segment of str1 which consists entirely of characters not in str2.
15	char *strerror(int errnum) Searches an internal array for the error number errnum and returns a pointer to an error message string.
16	size_t strlen(const char *str) Computes the length of the string str up to but not including the terminating null character.
17	char *strpbrk(const char *str1, const char *str2) Finds the first character in the string str1 that matches any character specified in str2.
18	char *strrchr(const char *str, int c) Searches for the last occurrence of the character c (an unsigned char) in the string pointed to by the argument str.
19	size_t strspn(const char *str1, const char *str2) Calculates the length of the initial segment of str1which consists entirely of characters in str2.
20	char *strstr(const char *haystack, const char *needle) Finds the first occurrence of the entire string needle(not including the terminating null character) which appears in the string haystack.
21	char *strtok(char *str, const char *delim) Breaks string str into a series of tokens separated by delim.
22	size_t strxfrm(char *dest, const char *src, size_t n) Transforms the first n characters of the string src into current locale and places them in the string dest.

C Library - < stdlib.h >

The stdlib.h header defines four variable types, several macros, and various functions for performing general functions.

Library Variables

Following are the variable types defined in the header stdlib.h −

Sr.No.	Variable & Description
1	size_t This is the unsigned integral type and is the result of the sizeof keyword.
2	wchar_t This is an integer type of the size of a wide character constant.
3	div_t This is the structure returned by the div function.
4	ldiv_t This is the structure returned by the ldiv function.

Library Macros

Following are the macros defined in the header stdlib.h −

Sr.No.	Macro & Description
1	NULL This macro is the value of a null pointer constant.
2	EXIT_FAILURE This is the value for the exit function to return in case of failure.
3	EXIT_SUCCESS This is the value for the exit function to return in case of success.
4	RAND_MAX This macro is the maximum value returned by the rand function.
5	MB_CUR_MAX This macro is the maximum number of bytes in a multi-byte character set which cannot be larger than MB_LEN_MAX.

Library Functions

Following are the functions defined in the header stdio.h −

Sr.No.	Function & Description
1	double atof(const char *str) Converts the string pointed to, by the argument str to a floating-point number (type double).
2	int atoi(const char *str) Converts the string pointed to, by the argument str to an integer (type int).
3	long int atol(const char *str) Converts the string pointed to, by the argument str to a long integer (type long int).
4	double strtod(const char *str, char **endptr) Converts the string pointed to, by the argument str to a floating-point number (type double).
5	long int strtol(const char *str, char **endptr, int base) Converts the string pointed to, by the argument str to a long integer (type long int).
6	unsigned long int strtoul(const char *str, char **endptr, int base) Converts the string pointed to, by the argument str to an unsigned long integer (type unsigned long int).
7	void *calloc(size_t nitems, size_t size) Allocates the requested memory and returns a pointer to it.
8	void free(void *ptr Deallocates the memory previously allocated by a call to calloc, malloc, or realloc.
9	void *malloc(size_t size) Allocates the requested memory and returns a pointer to it.
10	void *realloc(void *ptr, size_t size) Attempts to resize the memory block pointed to by ptr that was previously allocated with a call to mallocor calloc.
11	void abort(void) Causes an abnormal program termination.
12	int atexit(void (*func)(void)) Causes the specified function func to be called when the program terminates normally.
13	void exit(int status) Causes the program to terminate normally.
14	char *getenv(const char *name) Searches for the environment string pointed to by name and returns the associated value to the string.
15	int system(const char *string) The command specified by string is passed to the host environment to be executed by the command processor.
16	void *bsearch(const void *key, const void *base, size_t nitems, size_t size, int (*compar)(const void *, const void *)) Performs a binary search.
17	void qsort(void *base, size_t nitems, size_t size, int (*compar)(const void *, const void*)) Sorts an array.
18	int abs(int x) Returns the absolute value of x.
19	div_t div(int numer, int denom) Divides numer (numerator) by denom (denominator).
20	long int labs(long int x) Returns the absolute value of x.
21	ldiv_t ldiv(long int numer, long int denom) Divides numer (numerator) by denom (denominator).
22	int rand(void) Returns a pseudo-random number in the range of 0 to RAND_MAX.
23	void srand(unsigned int seed) This function seeds the random number generator used by the function rand.
24	int mblen(const char *str, size_t n) Returns the length of a multibyte character pointed to by the argument str.
25	size_t mbstowcs(schar_t *pwcs, const char *str, size_t n) Converts the string of multibyte characters pointed to by the argument str to the array pointed to by pwcs.
26	int mbtowc(whcar_t *pwc, const char *str, size_t n) Examines the multibyte character pointed to by the argument str.
27	size_t wcstombs(char *str, const wchar_t *pwcs, size_t n) Converts the codes stored in the array pwcs to multibyte characters and stores them in the string str.
28	int wctomb(char *str, wchar_t wchar) Examines the code which corresponds to a multibyte character given by the argument wchar.

C Library - < stdio.h >

The stdio.h header defines three variable types, several macros, and various functions for performing input and output.

Library Variables

Following are the variable types defined in the header stdio.h −

Sr.No.	Variable & Description
1	size_t This is the unsigned integral type and is the result of the sizeof keyword.
2	FILE This is an object type suitable for storing information for a file stream.
3	fpos_t This is an object type suitable for storing any position in a file.

Library Macros

Following are the macros defined in the header stdio.h −

Sr.No.	Macro & Description
1	NULL This macro is the value of a null pointer constant.
2	_IOFBF, _IOLBF and _IONBF These are the macros which expand to integral constant expressions with distinct values and suitable for the use as third argument to the setvbuffunction.
3	BUFSIZ This macro is an integer, which represents the size of the buffer used by the setbuf function.
4	EOF This macro is a negative integer, which indicates that the end-of-file has been reached.
5	FOPEN_MAX This macro is an integer, which represents the maximum number of files that the system can guarantee to be opened simultaneously.
6	FILENAME_MAX This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible filename. If the implementation imposes no limit, then this value should be the recommended maximum value.
7	L_tmpnam This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible temporary filename created by the tmpnamfunction.
8	SEEK_CUR, SEEK_END, and SEEK_SET These macros are used in the fseek function to locate different positions in a file.
9	TMP_MAX This macro is the maximum number of unique filenames that the function tmpnam can generate.
10	stderr, stdin, and stdout These macros are pointers to FILE types which correspond to the standard error, standard input, and standard output streams.

Library Functions

Following are the functions defined in the header stdio.h −

Follow the same sequence of functions for better understanding and to make use of Try it(Online compiler) option, because file created in the first function will be used in subsequent functions.

Sr.No.	Function & Description
1	int fclose(FILE *stream) Closes the stream. All buffers are flushed.
2	void clearerr(FILE *stream) Clears the end-of-file and error indicators for the given stream.
3	int feof(FILE *stream) Tests the end-of-file indicator for the given stream.
4	int ferror(FILE *stream) Tests the error indicator for the given stream.
5	int fflush(FILE *stream) Flushes the output buffer of a stream.
6	int fgetpos(FILE *stream, fpos_t *pos) Gets the current file position of the stream and writes it to pos.
7	FILE *fopen(const char *filename, const char *mode) Opens the filename pointed to by filename using the given mode.
8	size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream) Reads data from the given stream into the array pointed to by ptr.
9	FILE *freopen(const char *filename, const char *mode, FILE *stream) Associates a new filename with the given open stream and same time closing the old file in stream.
10	int fseek(FILE *stream, long int offset, int whence) Sets the file position of the stream to the given offset. The argument offset signifies the number of bytes to seek from the given whence position.
11	int fsetpos(FILE *stream, const fpos_t *pos) Sets the file position of the given stream to the given position. The argument pos is a position given by the function fgetpos.
12	long int ftell(FILE *stream) Returns the current file position of the given stream.
13	size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream) Writes data from the array pointed to by ptr to the given stream.
14	int remove(const char *filename) Deletes the given filename so that it is no longer accessible.
15	int rename(const char *old_filename, const char *new_filename) Causes the filename referred to, by old_filename to be changed to new_filename.
16	void rewind(FILE *stream) Sets the file position to the beginning of the file of the given stream.
17	void setbuf(FILE *stream, char *buffer) Defines how a stream should be buffered.
18	int setvbuf(FILE *stream, char *buffer, int mode, size_t size) Another function to define how a stream should be buffered.
19	FILE *tmpfile(void) Creates a temporary file in binary update mode (wb+).
20	char *tmpnam(char *str) Generates and returns a valid temporary filename which does not exist.
21	int fprintf(FILE *stream, const char *format, ...) Sends formatted output to a stream.
22	int printf(const char *format, ...) Sends formatted output to stdout.
23	int sprintf(char *str, const char *format, ...) Sends formatted output to a string.
24	int vfprintf(FILE *stream, const char *format, va_list arg) Sends formatted output to a stream using an argument list.
25	int vprintf(const char *format, va_list arg) Sends formatted output to stdout using an argument list.
26	int vsprintf(char *str, const char *format, va_list arg) Sends formatted output to a string using an argument list.
27	int fscanf(FILE *stream, const char *format, ...) Reads formatted input from a stream.
28	int scanf(const char *format, ...) Reads formatted input from stdin.
29	int sscanf(const char *str, const char *format, ...) Reads formatted input from a string.
30	int fgetc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream.
31	char *fgets(char *str, int n, FILE *stream) Reads a line from the specified stream and stores it into the string pointed to by str. It stops when either (n-1) characters are read, the newline character is read, or the end-of-file is reached, whichever comes first.
32	int fputc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream.
33	int fputs(const char *str, FILE *stream) Writes a string to the specified stream up to but not including the null character.
34	int getc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream.
35	int getchar(void) Gets a character (an unsigned char) from stdin.
36	char *gets(char *str) Reads a line from stdin and stores it into the string pointed to by, str. It stops when either the newline character is read or when the end-of-file is reached, whichever comes first.
37	int putc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream.
38	int putchar(int char) Writes a character (an unsigned char) specified by the argument char to stdout.
39	int puts(const char *str) Writes a string to stdout up to but not including the null character. A newline character is appended to the output.
40	int ungetc(int char, FILE *stream) Pushes the character char (an unsigned char) onto the specified stream so that the next character is read.
41	void perror(const char *str) Prints a descriptive error message to stderr. First the string str is printed followed by a colon and then a space.