c and math functions

davidleroux1 · 05-09-2005, 06:57 PM

using k develop (and new to c programing and kdevelop)

I wrote a program with the following two lines of code
I get the following errors. I wrote the "log" and "exp" as
math functions and I do have a line of code at the top stating

#include <math.h>

loc1 = (- 10.795) * (1.0 - loc1) - 2.1835 * log(loc1) + 2.2195;
loc1 = 29.9 * 1.0 / exp(2.3025 * loc1);

/home/david/enthalpy/src/enthalpy.c:94: undefined reference to `log'
enthalpy.o(.text+0x2d3):/home/david/enthalpy/src/enthalpy.c:95: undefined reference to `exp'

why are these math functions not working

Dark_Helmet · 05-09-2005, 07:26 PM

When you compile, you need to add "-lm" to the command line whenever you use functions from the math library. I don't know how you would do this with Kdevelop, but that's likely what your problem is.

davidleroux1 · 05-09-2005, 08:11 PM

now i get a parse error whenever i add "-lm" or just -lm
anywher in the code

any good tutorials on c programming in linux

Dark_Helmet · 05-09-2005, 09:03 PM

You misunderstand. The "-lm" does not go in your code. It is an option to give to the compiler. Kdevelop should have some sort of setting or menu somewhere that you can give extra options when the code is compiled. I don't use Kdevelop, so I can't say where that menu is. You'll have to hunt for it, look in the Kdevelop documentation, or wait for someone to come by and say where it is.

As for C tutorials, just do a search on Google. I'd actually go to www.google.com/linux and search for "C tutorial" or something along those lines. There should be tons of them out there. Or you can pick up a book. There are tons of those out there too

davidleroux1 · 05-09-2005, 10:25 PM

I found a place for project options with

configure, run, and make options.
lots of places to put things but does anyone know?

would it be easyer to compile from command interpreter
eg. gcc -lm program-file

new to using linux compilers

Dark_Helmet · 05-09-2005, 10:36 PM

Quote:

would it be easyer to compile from command interpreter
eg. gcc -lm program-file

To be honest, that's the way I program... emacs and the command line.

Contents of simple_prog.c:

Code:

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

int main( int argc, char *argv[] )
{
  double loc1;

  loc1 = 0.5;

  loc1 = (- 10.795) * (1.0 - loc1) - 2.1835 * log(loc1) + 2.2195;
  loc1 = 29.9 * 1.0 / exp(2.3025 * loc1);

  fprintf( stdout,
           "loc1 = %f\n",
           loc1 );

  return 0;
}

Compile command:

Code:

 gcc -lm -o simple_prog simple_prog.c

And run the result like so:

Code:

 ./simple_prog

davidleroux1 · 05-09-2005, 11:11 PM

I'll try it with out using k develop

__J · 05-10-2005, 06:28 AM

I believe -lm will have to go at the end of your gcc command for the linker to pick it up, or it will be mistaken for a gcc option.

fabianrios · 09-14-2006, 09:47 PM

For Kdevelop go to:

Project>Project Options>Configure Options>C>Compiler flags

Add -lm in the compiler flags