Adding user defined functions in C Library

Adding user-defined functions in C Library

In this article, I am going to discuss the Adding user-defined functions in C Library with an example. Please read our previous articles, where we discussed the Recursive Functions in C.

How to Add user-defined functions in C Library?
  1. Do you know that we can add our own user-defined functions to the C library?
  2. Yes. It is possible to add, delete, modify, and access our own user-defined function to or from the C library.
  3. The advantage of adding a user-defined function in the C library is, that this function will be available for all C programs once added to the C library.
  4. We can use this function in any C program as we use other C library functions.
  5. In the latest version of GCC compilers, compilation time can be saved since these functions are available in the library in the compiled form.
  6. Normal header files are saved as “file_name.h” in which all library functions are available. These header files contain source code and this source code is added in the main C program file where we add this header file using the “#include <file_name.h>” command.
  7. Whereas, precompiled versions of header files are saved as “file_name.gch”.
Steps for adding our own functions in C Library:

STEP 1: For example, below is a sample function that is going to be added to the C library. Write the below function in a file and save it as “addition.c”

addition(int i, int j)
    int total;
    total = i + j;
    return total;

STEP 2: Compile the “addition.c” file by using Alt + F9 keys (in turbo C).

STEP 3: “addition.obj” file would be created which is then compiled form of the “addition.c” file.

STEP 4: Use the below command to add this function to the library (in turbo C).
c:\> tlib math.lib + c:\ addition.obj
+ means adding c:\addition.obj file in the math library.
We can delete this file using – (minus).

STEP 5: Create a file “addition.h” & declare prototype of addition() function like below.
int addition (int i, int j);

Now, the addition.h file contains a prototype of the function “addition”.

Note: Please create, compile, and add files in the respective directory as the directory name may change for each IDE.

STEP 6: Let us see how to use our newly added library function in a C program.

# include <stdio.h> // Including our user defined function.
# include “c:\\addition.h”
int main ()
    int total;
    // calling function from library
    total = addition (10, 20);
    printf ("Total = %d \n", total);

Output: Total = 30

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