Strange compiler error

**Suchy** · 10-25-2008

When trying to compile a simple script with Gcc:

Code:

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

int main()
{
	double a = cos(360);
	printf ("cos: %d\n\n", a);

	double b = sin(360);
	printf ("sin: %d\n\n", b);

	double c = tan(45);
	printf ("tan: %d\n\n", c);

	return 0;
}

I get an error:

/tmp/cckLVeVp.o: In function `main':
trig.c

.text+0x1b): undefined reference to `cos'
trig.c

.text+0x3f): undefined reference to `sin'
trig.c

.text+0x63): undefined reference to `tan'
collect2: ld returned 1 exit status

I compile via: gcc trig.c -o test, however when I compile using
g++ trig.c -o test it works.

Why is it compiling with c++ compiler and not c compiler since it is a c script ????

**Elysia** · 10-25-2008

It seems you are failing to link with the C standard library. Consult the docs on how to do that.

**tabstop** · 10-25-2008

And of course Elysia means the math library, not the standard library. To link the math library, add -lm to the end of your gcc command line.

**Elysia** · 10-25-2008

Originally Posted by tabstop

And of course Elysia means the math library, not the standard library. To link the math library, add -lm to the end of your gcc command line.

Duh, how am I supposed to know of a compiler that keeps two separate libraries?
I'm living in the current and don't need to type commands from the command line to compile or link to whatever-you-call-it libraries. I push a simple button and it works. That is today.
Hmph.

**matsp** · 10-25-2008

Actually, what compiler needs what switches depends on both the compiler and the library implementation. The glibc that is used with Linux has a separate math library (which has the benefit that it can be replaced with a different math library, should someone wish to do so).

--
Mats

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