C Library Function

Table of Contents

C library functions, also known as C standard library functions, are built-in functions in C programming.
These functions’ prototypes and data definitions can be found in their respective header files.
We must include the header file in our program in order to use these functions.
For example, if you want to use the printf() function, you must include the header file <stdio.h>.

String Function

strcpy
strncpy
strcat
strncat
strchr

Mathematical Function

acos
asin
atan
ceil
cos

Date & Time Function

clock
difftime
mktime
time
asctime

I/O Formatting Functions

printf
scanf
getc
getchar
gets

Miscellaneous Functions

delay
clrscr
clearer
isalpha
isalnum
isdigit
islower

Standard Library functions

abs
atof
atol
exit
free
labs
rand

Memory Allocation Functions

malloc
realloc
calloc

Summary of Header Files

Header file	Full Name	Explanation
<stdio.h>	Standard input-output header	Used to perform input and output operations like scanf() and printf()
<string.h>	String header	Used to perform string manipulation operations like strlen and strcpy.
<conio.h>	Console input-output header	Used to perform console input and console output operations like clrscr() to clear the screen and getch() to get the character from the keyboard.
<stdlib.h>	Standard library header	Used to perform standard utility functions like dynamic memory allocation using functions such as malloc() and calloc().
<math.h>	Math header	Used to perform mathematical operations like sqrt() and pow() to obtain the square root and the power of a number respectively.
<ctype.h>	Character type header	Used to perform character type functions like isaplha() and isdigit() to find whether the given character is an alphabet or a digit. respectively.
<time.h>	Time header	Used to perform functions related to date and time like setdate() and getdate() to modify the system date and get the CPU time respectively.
<assert.h>	Assertion header	Used in program assertion functions like assert() to get an integer data type as a parameter which prints stderr only if the parameter passed is 0.
<locale.h>	Localization header	Used to perform localization functions like setlocale() and localeconv() to set locale and get locale conventions respectively.
<signal.h>	Signal header	Used to perform signal handling functions like signal() and raise() to install signal handler and to raise the signal in the program respectively.
<setjmp.h>	Jump header	Used to perform jump functions.
<stdarg.h>	Standard argument header	Used to perform standard argument functions like va_start and va_arg() to indicate the start of the variable-length argument list and to fetch the arguments from the variable-length argument list in the program respectively.
<errno.h>	Error handling header	Used to perform error handling operations like errno() to indicate errors in the program by initially assigning the value of this function to 0 and then later changing it to indicate errors.