Standard Functions in C

The standard functions are built-in functions. In C programming language, the standard functions are declared in header files and defined in .dll files. In simple words, the standard functions can be defined as "the ready made functions defined by the system to make coding more easy". The standard functions are also called as library functions or pre-defined functions.

In C when we use standard functions, we must include the respective header file using #include statement. For example, the function printf() is defined in header file stdio.h (Standard Input Output header file). When we use printf() in our program, we must include stdio.h header file using #include<stdio.h> statement.

C Programming Language provides the following header files with standard functions.

Header File Purpose Example Functions
stdio.h Provides functions to perform standard I/O operations printf(), scanf()
conio.h Provides functions to perform console I/O operations clrscr(), getch()
math.h Provides functions to perform mathematical operations sqrt(), pow()
string.h Provides functions to handle string data values strlen(), strcpy()
stdlib.h Provides functions to perform general functions calloc(), malloc()
time.h Provides functions to perform operations on time and date time(), localtime()
ctype.h Provides functions to perform - testing and mapping of character data values isalpha(), islower()
setjmp.h Provides functions that are used in function calls setjump(), longjump()
signal.h Provides functions to handle signals during program execution signal(), raise()
assert.h Provides Macro that is used to verify assumptions made by the program assert()
locale.h Defines the location specific settings such as date formats and currency symbols setlocale()
stdarg.h Used to get the arguments in a function if the arguments are not specified by the function va_start(), va_end(), va_arg()
errno.h Provides macros to handle the system calls Error, errno
float.h Provides constants related to floating point data values
limits.h Defines the maximum and minimum values of various variable types like char, int and long
stddef.h Defines various variable types
graphics.h Provides functions to draw graphics. circle(), rectangle()