General functions of C language

First, mathematical functions

When a mathematical function is called, the following command line is required to be wrapped in the source file:

#include <math.h>

Function prototype Description	Function	return value	Description
int abs (int x)	To find the absolute value of an integer x	Calculation results
Double fabs (Double x)	Finding the absolute value of a double-precision real X	Calculation results
Double ACOs (Double x)	Calculates the value of Cos-1 (x)	Calculation results	x within the -1~1 range
Double asin (Double x)	Calculates the value of sin-1 (x)	Calculation results	x within the -1~1 range
Double Atan (Double x)	Calculates the value of tan-1 (x)	Calculation results
Double atan2 (Double x)	Calculates the value of the tan-1 (x/y)	Calculation results
Double cos (double x)	Calculate the value of the cos (x)	Calculation results	The units of X are in radians
Double cosh (Double x)	Computes the value of the hyperbolic cosine cosh (x)	Calculation results
Double exp (Double x)	Find the value of ex	Calculation results
Double fabs (Double x)	Finding the absolute value of a double-precision real X	Calculation results
Double floor (Double x)	The maximum integer that is not greater than the double-precision real X
Double Fmod (double x,double y)	Finding the double-precision remainder after X/Y division
Double Frexp (double val,int *exp)	The double Val decomposes the mantissa and the 2-based exponent N, that is, the val=x*2n,n is stored in the variable that the exp refers to	Return number of Bits X 0.5≤x<1
Double log (double x)	Beg ㏑x	Calculation results	X>0
Double log10 (Double x)	Beg log10x	Calculation results	X>0
Double modf (double val,double *ip)	The double Val is decomposed into an integer part and a fractional part, and the integer portion is stored in the variable referred to by the IP.	Returns the number of decimal points
Double pow (double x,double y)	Calculate the value of XY	Calculation results
Double sin (double x)	Calculates the value of sin (x)	Calculation results	The units of X are in radians
Double Sinh (Double x)	Calculates the value of X's hyperbolic sine function sinh (x)	Calculation results
Double sqrt (double x)	Calculate the root of X	Calculation results	X≥0
Double tan (Double x)	Calculate tan (x)	Calculation results
Double Tanh (Double x)	Computes the value of the hyperbolic tangent function of x tanh (x)	Calculation results

Second, character function

When calling the character function, the following command line is required to be wrapped in the source file:

#include <ctype.h>

Function prototype Description	Function	return value
int isalnum (int ch)	Check if CH is a letter or a number	Yes, returns 1; otherwise returns 0
int isalpha (int ch)	Check if CH is a letter	Yes, returns 1; otherwise returns 0
int Iscntrl (int ch)	Check if CH is a control character	Yes, returns 1; otherwise returns 0
int isdigit (int ch)	Check if CH is a number	Yes, returns 1; otherwise returns 0
int isgraph (int ch)	Check if CH is an ASCII value in ox21 to ox7e printable character (that is, does not contain a space character)	Yes, returns 1; otherwise returns 0
int islower (int ch)	Check if CH is a lowercase letter	Yes, returns 1; otherwise returns 0
int isprint (int ch)	Check if CH is a printable character, including whitespace	Yes, returns 1; otherwise returns 0
int ispunct (int ch)	Check if CH is a printable character other than spaces, letters, numbers	Yes, returns 1; otherwise returns 0
int isspace (int ch)	Check if CH is a space, tab, or line break	Yes, returns 1; otherwise returns 0
int isupper (int ch)	Check if CH is an uppercase letter	Yes, returns 1; otherwise returns 0
int isxdigit (int ch)	Check if CH is 16 binary number	Yes, returns 1; otherwise returns 0
int tolower (int ch)	Convert the letters in CH into lowercase letters	Returns the corresponding lowercase letter
int toupper (int ch)	Convert the letters in CH to uppercase	Returns the corresponding uppercase letter

Three, String function

When calling the character function, the following command line is required to be wrapped in the source file:

#include <string.h>

Function prototype Description	Function	return value
Char *strcat (char *s1,char *s2)	S2 string to S1 back	Address referred to by S1
Char *strchr (char *s,int ch)	Find the position of the first occurrence of the character ch in the S-referred string	Returns the address of the found character, no return null found
int strcmp (char *s1,char *s2)	Comparison of strings referred to by S1 and S2	S1<S2, returns a negative number; s1= =s2, returns 0;S1>S2, returns a positive number
Char *strcpy (char *s1,char *s2)	Copy the string that S2 points to the space that S1 points to	Address referred to by S1
unsigned strlen (char *s)	To find the length of the string s	Returns the number of characters in a string (not counting the last ' s ')
Char *strstr (char *s1,char *s2)	In the string S1, find the first occurrence of the string s2	Returns the address of the found string, no return null found

Iv. input and OUTPUT functions

When calling the character function, the following command line is required to be wrapped in the source file:

#include <stdio.h>

Function prototype Description	Function	return value
void clearer (FILE *fp)	Clears all error messages related to the file pointer fp	No
int fclose (FILE *fp)	Closes the file referred to by the FP, releasing the file buffer	Error returns non 0, otherwise returns 0
int feof (FILE *fp)	Check if the file ends	Returns 0 if the end of the file is not returned, otherwise 0
int fgetc (FILE *fp)	Get the next character from the file referred to in the FP	Error returns EOF, otherwise the read character is returned
Char *fgets (char *buf,int N, FILE *FP)	Reads a string of length n-1 from the file referred to by the FP and stores it in the BUF-referred storage area	Returns the address referred to by BUF, or returns null if the file ends or an error occurs
FILE *fopen (char *filename,char *mode)	Open a file named filename in the mode specified by mode	Successful, returns the file pointer (the start address of the file information area), otherwise returns null
int fprintf (FILE *fp, Char *format, args,...)	,... the Args Output to the FP-specified file in the format specified by format	The actual number of characters to output
int FPUTC (char ch, FILE *FP)	Output ch characters to the FP-specified file	The character is returned successfully, or EOF is returned
int fputs (char *str, FILE *FP)	Outputs the string str refers to the file referred to in the FP	A non-negative integer was returned successfully, otherwise 1 (EOF)
int fread (char *pt,unsigned size,unsigned N, FILE *FP)	Reads the length from the FP-referred file size to n data items to a PT-referred file	Number of data items read
int fscanf (FILE *fp, char *format,args,...)	The input data is deposited into the args,... in the format specified by format in the file referred to by the FP. Referred to in-memory	Number of data entered, end of file or error returned 0
int fseek (FILE *fp,long offer,int Base)	Position pointer of the file moved by the FP	The current position is returned successfully, otherwise 0 is not returned
Long Ftell (FILE *FP)	Find the current read and write location of the file referred to by the FP	Read and write location, error return -1l
int fwrite (char *pt,unsigned size,unsigned N, FILE *FP)	Enter the N*size bytes pointed to by PT into the file referred to in the FP	Number of data items to output
int getc (FILE *fp)	Reads a character from a file that is referred to in the FP	Returns the read character, if an error occurs or the end of the file returns EOF
int GetChar (void)	Reading the next character from a standard input device	Returns the read character, if an error occurs or the end of the file returns-1
Char *gets (char *s)	Reads a line of string from a standard device into the storage area referred to by S, replacing the read-in line break with '% '	Returns s, error returns null
int printf (char *format,args,...)	,... the Args Output to a standard output device in the format specified by format	Number of output characters
int PUTC (int ch, FILE *FP)	With FPUTC	With FPUTC
int Putchar (char ch)	Output ch to standard output device	Returns the character of the output, or EOF if an error occurs
Int puts (char *str)	Output the STR string to the standard device and convert '% ' to carriage return newline.	Returns the newline character, in case of an error, returns EOF
int rename (char *oldname,char *newname)	Change the file name referred to Oldname to the name of NewName	Successfully returned 0, error returned-1
void Rewind (FILE *fp)	Place the file position pointer at the beginning of the file	No
int scanf (char *format,args,...)	The input data is deposited into the args from the standard input device in the format specified by format,... Referred to in-memory	The number of data that has been entered

V. Dynamic allocation functions and random functions

When calling the character function, the following command line is required to be wrapped in the source file:

#include <stdlib.h>

Function prototype Description	Function	return value
void *calloc (unsigned n,unsigned size)	Allocates the memory space of n data items, each data item size is a byte	The starting address of the allocated memory unit; If unsuccessful, returns 0
void *free (void *p)	Releasing the memory area referred to by P	No
void *malloc (unsigned size)	Allocate a size byte of storage space	The address of the allocated memory space; If unsuccessful, returns 0
void *realloc (void *p,unsigned size)	Changes the size of the memory area referred to as p to size bytes	The address of the newly allocated memory space; If unsuccessful, returns 0
int rand (void)	Random integers that produce 0~32767	Returns a random integer
void exit (int state)	The program terminates execution, returns the calling procedure, state is 0 normal termination, non 0 non-normal termination	No

Implementation code for C-language standard library functions

C language Common functions Daquan