undefined reference to `cos'

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Hi,

I have the code below:

C++

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

int main(int argc, char **argv){

float index;
	for(index = 0; index <= 360; index++){
		index = (3.14/180) * index; //convert to radiant
		float a = cos(index);
		printf("a = %f\n", a);
	}
}

And when I tried to compile, I got the error below:

/tmp/ccEPoXwg.o: In function `main':
test.c:(.text+0x6b): undefined reference to `cos'
collect2: ld returned 1 exit status

What is weird is that when I try this (without the for loop) :

C++

float a = cos(3.14);
  printf("a = %f\n", a);

I get no errors

Can anyone, please help me.

Thank you in advance

Posted 19-Dec-10 4:32am

The_Real_Chubaka

Updated 19-Dec-10 4:52am

Henry Minute

v2

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3 solutions

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pasztorpisti · Accepted Answer · 2010-12-19T06:11:00

Solution 2

The problem is that you have only a cos(double) function in your math library but you are trying to call a cos(float) function in the loop. Without the loop you pass a double type number to cos() (because you say cos(3.14) and not cos(3.14f)). But in the loop you pass in a float (float index). Declare index as a double or cast index to a double when you call cos()!

Most math libraries contain a cos(double) and a cosf(float) function. You can try using cosf() if you want to stick with your float data!

Posted 19-Dec-10 6:11am

pasztorpisti

Updated 19-Dec-10 6:24am

v3

Comments

Richard MacCutchan 19-Dec-10 15:54pm

Excellent answer, I certainly missed that subtle difference.

The_Real_Chubaka 20-Dec-10 4:57am

Thank you for you answer. The main mistake i made is that i forgot to link with the math library. I also did not know that there was no cos(float) function in the math library. Thank you for that information too.

CPallini · Accepted Answer · 2010-12-19T07:44:00

Solution 3

You must link with the math library, namely:

gcc myprogram.c -lm

:)

Posted 19-Dec-10 7:44am

CPallini

Comments

The_Real_Chubaka 20-Dec-10 4:59am

Thank you. I did what you suggested.
My code works now.

Lightning Monster 18-Dec-22 15:11pm

WTF My library is not working and I am finding a solution for this error for a week its solution is only type -lm when compiling!! BTW Thank U sir/madam!!

Richard MacCutchan · Accepted Answer · 2010-12-19T05:25:00

Solution 1

~~Check your build statement, or make script, to ensure that you are including the correct math library in your link phase.~~

pasztorpisti has the correct answer; well done considering the sample does not use Hungarian notation. :laugh:

Posted 19-Dec-10 5:25am

Richard MacCutchan

Updated 19-Dec-10 9:57am

v2

Comments

The_Real_Chubaka 20-Dec-10 4:58am

Thank you for you answer. The code work now.
I just forgot to link with the math library.