C Standard Library 简明教程

C Library - <stdlib.h>

stdlib.h 头定义了四种变量类型、几个宏和各种函数，用于执行通用函数。

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

Library Variables

以下是在头文件 stdlib.h 中定义的变量类型−

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

以下是 stdlib.h 头中定义的宏 −

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

以下是头文件 stlib.h 中定义的函数 −

Following are the functions defined in the header stlib.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 *ptrDeallocates 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 malloc or 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.