Some library functions, constants, and header files commonly used in C + +

1 , common mathematical functions

Header file #include <math> or #include <math.h>

Function prototypes	Function	return value
int abs (int x)	To find the absolute value of an integer x	Absolute
Double ACOs (Double x)	Calculates the value of Arcos (x)	Calculation results
Double asin (Double x)	Calculates the value of Arsin (x)	Calculation results
Double Atan (Double x)	Calculates the value of arctan (x)	Calculation results
Double cos (double x)	Calculate the value of the cos (x)	Calculation results
Double cosh (Double x)	Computes the value of the hyperbolic cosine cosh (x) of X	Calculation results
Double exp (Double x)	The value of the request	Calculation results
Double fabs (Double x)	Absolute value of realistic number X	Absolute
Double Fmod (Double x)	Find the remainder of X/y	Double precision number of remainder
Long Labs (long X)	To find the absolute value of a long integer number	Absolute
Double log (double x)	Calculates the value of in (x)	Calculation results
Double log10 (Double x)	The calculated value	Calculation results
Double modf (double x, double *y)	Take the integer portion of x to the cell that Y points to	Small tree part of X
Double pow (double x, double y)	Find the value of X's Y-square	Calculation results
Double sin (double x)	Calculates the value of sin (x)	Calculation results
Double sqrt (double x)	The value of the request	Calculation results
Double tan (Double x)	Calculate the value of tan (x)	Calculation results
Fcvt	Convert a floating-point number to a string

2. String function (<string.h>)

String functions

All string functions are listed in the table below, and the function description takes the following conventions: S, T (char *) type parameters, CS, CT (const char*) type parameters (they all should represent strings). n represents a parameter of type size_t (size_t is an unsigned integer type), and C is an integer parameter (converted to char in a function):

Function prototypes	Meaning explanation
size_t strlen (CS)	Find the length of CS (not including ' strlen '), such as Chai =4
Char *strcpy (S,CT)	Copy the CT to S. Requires S to specify a large enough character array
Char *strncpy (s,ct,n)	Copy up to n characters from the CT to S. Requires S to specify a character array that is large enough. If the characters in the CT are not enough n, fill the empty characters in S.
Char *strcat (S,CT)	Copy the characters in the CT to the existing string in S. s should specify a character array that holds the string and is large enough.
Char *strncat (s,ct,n)	Copy up to n characters in CT to the existing string in S. s should specify a character array that holds the string and is large enough.
int strcmp (CS,CT)	Compare the size of the string CS and CT, return positive, 0, negative values when CS is greater than, equal to, and less than Ct.
int strncmp (CS,CT,N)	Compares the size of the string CS and CT to a maximum of n characters. When CS is greater than, equal to, less than CT, return positive, 0, negative value respectively.
Char *STRCHR (CS,C)	Searches for C in CS and returns the position of the first occurrence of C, expressed as a pointer to the position. return value NULL if C is not in CS
Char *STRRCHR (CS,C)	Searches for C in CS and returns the position of the last occurrence of C, and returns null if no
size_t strspn (CS,CT)	A sequence of all the characters in the CT that is determined by CS to return its length
size_t strcspn (CS,CT)	A sequence of all non-CT characters determined by CS to return its length
Char *strpbrk (CS,CT)	Searches for the characters in the CT in CS, returns the position of the first character that satisfies the condition, and returns null if none is present
Char *strstr (CS,CT)	Search for string CT (query substring) in CS, return the first occurrence of CT as a substring of CS, return NULL if CT does not appear in CS
Char *strerror (n)	Returns the error message string associated with error number n (pointer to the error message string)
Char *strtok (S,CT)	Search for words in s that are formed by characters in CT as separators

Store Operations

<string.h> also has a set of character array manipulation functions (store manipulation functions) whose names start with Mem and are implemented in an efficient manner. In the following prototype, the type of the parameter S and T is (void *), the type of CS and CT is (const void *), the type of n is the size_t,c type is int (converted to unsigned char).

Function prototypes	Meaning explanation
void *memcpy (S,ct,n)	Copy n characters from CT to S, return s
void *memmove (S,ct,n)	Copy n characters from CT to S, return s, two segments here allow overlap
int memcmp (CS,CT,N)	Compare n characters starting with CS and CT, and return values defined with strcmp
void *memchr (Cs,c,n)	Searches for the first occurrence of C in CS in the range of n characters, returns the pointer value for that position if found, otherwise returns null
void *memset (S,c,n)	Set s first n characters to C, return s

3. header file #include <stdlib> or # include <stdlib.h>

Function prototypes	Function	return value	Description
void abort (void)	Terminating program execution		Can't finish the job.
void exit (int)	Terminating program execution		Finish the job.
Double atof (const char *s)	Converts the string that s points to a real number	Real value
int atoi (const char *s)	Converts the string that s points to an integer	Integer value
Long Atol (const char *s)	Converts the string referred to by S to grow integers	Long Integer value
int rand (void)	Produces a random integer	Random integers
void Srand (unsigned int)	Initializing the random number generator
int system (const char *s)	The string pointed to by S as an executable file and executed
Max (A, B)	Ask for a large number in two numbers	Large number	parameter is any type
Min (A, B)	Ask for a decimal in two numbers	Decimal	parameter is any type

4. Header Files <climits> or <limits.h>

name	expresses	min. magnitude*
Char_bit	Number of bits for a char object (Byte)	8
Schar_min	Minimum value for an object of type signed Char	-127
Schar_max	Maximum value for an object of type signed Char	127
Uchar_max	Maximum value for an object of type unsigned char	255
Char_min	Minimum value for an object of type char	Either schar_min or 0
Char_max	Maximum value for an object of type char	Either Schar_max or Uchar_max
Mb_len_max	Maximum number of bytes in a multibyte character, for any locale	1
Shrt_min	Minimum value for a object of type short int	-32767
Shrt_max	Maximum value for a object of type short int	32767
Ushrt_max	Maximum value for a object of type unsigned short int	65535
Int_min	Minimum value for an object of type int	-32767
Int_max	Maximum value for an object of type int	32767
Uint_max	Maximum value for a object of type unsigned short int	65535
Long_min	Minimum value for an object of type long int	-2147483647
Long_max	Maximum value for an object of type long int	2147483647
Ulong_max	Maximum value for an object of type unsigned int	4294967295

Some library functions, constants, and header files commonly used in C + +