: undefined reference to `pow'

[mohitsaxena019]

Hi all,

I am playing with pow() function using gcc compiler. I have got some intresting error while playing. Here I am writing the code as well as the problem

main()
{
int i,j,k;
j=10;
k=2;
i=pow(j,k);
printf("i=%d",i );
}
It is the Complete code no math directory included.
when i compile this using the following command:
gcc test.c
It gives the following error
/var/tmp//ccUP0AVk.o(.tex t+0x3f): In function `main':
: undefined reference to `pow'

when i compile this using the following command:
gcc -lm test.c
It gives no error and correct output

Now I had make some changes in the program

main()
{
int i,j,k;
j=10;
k=2;
i=pow(10,2);
printf("i=%d",i );
}

when i compile this using the following command:
gcc test.c
It gives no error and correct output

Q1:-) Is it not necessary to include files in the code.
Q2:-) Why it is not giving error in the second code.

Plz help me out.

[donbock]

A #include file provides information to the compiler that is used to convert one source file into one object file.

The -lm command-line switch provides information to the linker that is used to combine and convert one or more object files into an executable image file.

You should #include all relevant header files to insure consistent and repeatable operation of the compiler. In your specific case, the header files provide function prototypes for pow() and printf().

I don't know why the linker succeeded without -lm in your second example. It is a curiosity; I wouldn't worry about it.