pow() isn't defined

Question

#include <stdio.h>
#include <math.h>

void main()
{
    int i, diff, sum = 0, num1 = 6, num2 = 2;

    for(i = 0; i <= 4; i++)
    {
        diff = num1 - num2;
        sum += pow(diff, i);
    }

    printf("%d", sum);
}

Whenever I am trying to execute this program, an error message just pops up saying:

In function main:
undefined reference to pow.

What am I missing here?

See http://stackoverflow.com/questions/103407/why-am-i-getting-link-errors-when-calling-function-in-math-h — simonc, Oct 09 '12 at 14:24
It works as written for me with gcc 4.6.1 on Mac OSX. Prints out "341". What compiler and platform are you using? — Clark, Oct 09 '12 at 14:26
I hope you don't actually code like what you pasted in. FTFY. — Ry-, Oct 09 '12 at 14:26

score 12 · Accepted Answer · answered Oct 09 '12 at 14:23

12

This is a linker failure. You need to link with the math library, specify -lm at the end of your compiler command. From man pow:

Link with -lm.

answered Oct 09 '12 at 14:23

hmjd

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score 6 · Answer 2 · answered Oct 09 '12 at 14:24

6

Math library is not part of libc. You need to link it:

gcc file.c -lm -o file

answered Oct 09 '12 at 14:24

P.P

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score 0 · Answer 3 · answered Oct 09 '12 at 14:26

The function pow() is defined in the math library. Your compiler by default is not linking your program with that library as a result of which the linker is unable the resolve the call to pow().

To fix this you need to add -lm at the end of your compile/link line which links the math lib to your program.

score 0 · Answer 4 · answered Oct 09 '12 at 15:58

I just ran the same program on my Turbo C and i got output as 341. Check whether your header files are in place in /include folder of your Turbo C folder. Make sure to check whether it contains a Math.h file.

pow() isn't defined

4 Answers4

Linked

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