Re: Problem compiling simple C program

[Sven Joachim <svenjoac@gmx.de>]

On 2008-04-15 20:39 +0200, John Salmon wrote:

> I'm running Debian Etch on a PC. When I try to compile the following 
> (called test.c);
>
> #include <math.h>
> #include <stdio.h>
>
> int main()
> {
>     double
>         val = 1.55;
>
>     printf("sine: %g\n", sin(val));
>
>     return 0;
> }
>
> using the command line
>
> gcc -Wall -o test test.c
>
> I get
>
> /tmp/cciDV02m.o: In function `main':
> test.c:(.text+0x21): undefined reference to `sin'
> collect2: ld returned 1 exit status

You need to link to the math library by specifying -lm _at the end_ of
the gcc command line, otherwise the linker does not know about the sin()
function.

> When I compile the equivalent C++ program using the apropriate C++ 
> parameters, everything goes great. Have I neglected to load a Debian 
> package? Any help will be appreciated.

That is to be expected, because C++ programs are automatically linked
against the math library.  In C you have to tell the linker to use it
with -lm.

Sven