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Compiling C program with math.h library in Linux.

The solution is:
Use -lm after the compile command.

Please read complete article to learn better.

Compile C program with math.h in Linux

Many of the programmer's don't know how to compile a C program which is using math.h library functions? After including math.h header file, program does not compile and return error(s).

Let's understand with an example: Here is a program that will read an integer number and we want to get square root and cube of entered integer number.
As we are aware that sqrt() is used to get square root and pow() is used to get power of any number.

Program - number.c

#include <stdio.h>
#include <math.h>
 
int main()
{
    int num;
    float sqrRoot;
    long cube;
     
    printf("Enter any integer number: ");
    scanf("%d",&num);
     
    sqrRoot=sqrt(num);
    cube=pow(num,3);
 
    printf("Number: %d \nSquare Root: %f \nCube: %ld \n",num,sqrRoot,cube);
     
    return 0;
}

Now compile program as normally (as usual we compile any c program),

The compile command is:

gcc number.c -o number

program will throw an error, and the error is:

sh-4.3$ gcc number.c -o number
number.c: undefined reference to 'sqrt'
number.c: undefined reference to 'pow'

Then, how to compile C program with math.h library?

To compile C program with math.h library, you have to put -lm just after the compile command gcc number.c -o number, this command will tell to the compiler to execute program with math.h library.

The command is:

gcc number.c -o number -lm
  • gcc is the compiler command.
  • number.c is the name of c program source file.
  • -o is option to make object file.
  • number is the name of object file.
  • -lm is option to execute math.h library file.

See the output after running this command

sh-4.3$ gcc number.c -o number -lm
sh-4.3$ ./number
Enter any integer number: 3 
Number: 3 
Square Root: 1.732051 
Cube: 27
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