C – Library functions

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  • Library functions in C language are inbuilt functions which are grouped together and placed in a common place called library.
  • Each library function in C performs specific operation.
  • We can make use of these library functions to get the pre-defined output instead of writing our own code to get those outputs.
  • These library functions are created by the persons who designed and created C compilers.
  • All C standard library functions are declared in many header files which are saved as file_name.h.
  • Actually, function declaration, definition for macros are given in all header files.
  • We are including these header files in our C program using “#include<file_name.h>” command to make use of the functions those are declared in the header files.
  • When we include header files in our C program using “#include<filename.h>” command, all C code of the header files are included in C program. Then, this C program is compiled by compiler and executed.

Please check the below links for actual C source code for the respective C header files.

1. C – stdio.h source code

2. C – conio.h source code

3. C – string.h source code

4. C – stdlib.h source code

5. C – math.h source code

6. C – time.h source code

7. C – ctype.h source code

  • If you want to check source code for all header files, you can check inside “include” directory after C compiler is installed in your machine.
  • For example, if you install DevC++ compiler in C directory in your machine, “C:\Dev-Cpp\include” is the path where all header files will be available.

List of most used header files in C programming language:

  • Check the below table to know all the C library functions and header files in which they are declared.
  • Click on the each header file name below to know the list of inbuilt functions declared inside them.
Header file
stdio.h This is standard input/output header file in which Input/Output
functions are declared
conio.h This is console input/output header file
string.h All string related functions are defined in this header file
stdlib.h This header file contains general functions used in C programs
math.h All maths related functions are defined in this header file
time.h This header file contains time and clock related functions
ctype.h All character handling functions are defined in this header file
stdarg.h Variable argument functions are declared in this header file
signal.h Signal handling functions are declared in this file
setjmp.h This file contains all jump functions
locale.h This file contains locale functions
errno.h Error handling functions are given in this file
assert.h This contains diagnostics functions

Continue on C – User defined functions & adding them in C library….

Continue on C – Command line arguments….

Continue on C – Variable length arguments….

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