Re: Using Math Functions

Re: Using Math Functions

[Anjali Sharma]

Hi
  Trying using  "-lm" while linking your program

Hope this helps
Anjali

uucp-relay-delhi!calvesmit@ig.com.br wrote:

> I'm trying to compile the code below, but I can't to do it! gcc always
> complain.
> could someone help me? Why my sistem seems not know about math functions
> althoug i use #include math.h inclusion.
> send any hint to calvesmit@ig.com.br, 'cause I'm not a subscribe of your
> list.
>
> **********CODE***********
> #include <stdio.h>
> #include <stdlib.h>
> #include <math.h>
>
> int main(int argc,char *argv[])
> {
>         int i;
>         if(argc==2){
>                 i=atoi(argv[1]);
>                 printf("sin(%i)=%0.2f\n",i,sin(i));}
>         return 0;
> }
>
> **************ERROR MESSAGE*************
> $gcc sin.c -osin
> /root/tmp/ccpbz3XU.o: In function 'main':
> /root/tmp/ccpbz3XU.o(.text+0x32): undefined reference to 'sqrt'
> collect2: ld returned 1 exit status
>
> _________________________________________________________
> Voce quer um iGMail protegido contra vírus e spams?
> Clique aqui: http://www.igmailseguro.ig.com.br

Re: Using Math Functions

[Tkil]

>>>>> "Tkil" == tkil  <tkil@scrye.com> writes:

Tkil> Or, if you have multiple files:

Tkil>    gcc -c my_lib.c
Tkil>    gcc -c my_prog.c
Tkil>    gcc -o my_prog my_lib.o my_prog.o -lm
                        ^^^^^^^^ ^^^^^^^^^^

Open foot, insert mouth.  Assuming my_prog.c calls routines in
my_lib.c, it needs to be the other way around:

   gcc -o my_prog my_prog.o my_lib.o -lm

Tkil> Note that "-lm" should be after any of your object files that
Tkil> use functions from it, as symbols are resolved from
Tkil> left-to-right on the command line.

I even knew that.

t.

Re: Using Math Functions

[Tkil]

[copied back to gcc list, so that nobody else sends this FGA]

>>>>> "calvesmit" == calvesmit  <calvesmit@ig.com.br> writes:

calvesmit> I'm trying to compile the code below, but I can't to do it! 
calvesmit> gcc always complain. could someone help me? Why my sistem
calvesmit> seems not know about math functions althoug i use #include
calvesmit> math.h inclusion. send any hint to calvesmit@ig.com.br,
calvesmit> 'cause I'm not a subscribe of your list.

Short answer: you need "-lm" at the end of your gcc line.

Longer answer:

Using "#include <math.h>" only brings in the *declarations* of the
functions (type of arguments, type of return); it doesn't bring in the
*definition* or *implementation* of the functions.  Those are stored
in the math library, "libm.a" or "libm.so".  You link these in by
using "-lm" on your compile line:

   gcc -o my_prog my_prog.c -lm

Or, if you have multiple files:

   gcc -c my_lib.c
   gcc -c my_prog.c
   gcc -o my_prog my_lib.o my_prog.o -lm

Note that "-lm" should be after any of your object files that use
functions from it, as symbols are resolved from left-to-right on the
command line.

Next time, consider searching the web before posting; a quick search
for the text of your error gave me the answer on the second hit.
(Granted, I already *knew* the answer, but hey...)

Finally, note that this list (<gcc@gcc.gnu.org>) is explicitly for the
development of GCC itself -- it is not for developing *with* gcc; your
question would be better answered on comp.lang.c or similar fora.

Oh, and the really last thing: bookmark Google, and use it often (I do
understand that you might not be on the 'net full time, but you were
on long enough to send e-mail); also, consult the C FAQ, which is a
very helpful document:

   http://www.eskimo.com/~scs/C-faq/top.html

Regarding your question in particular:

   http://www.eskimo.com/~scs/C-faq/q14.3.html

If you get the chance, please read the entire document.  You might not
understand all of it the first time through, but it will hopefully
live in your memory; the next time you have a question, you might
remember where to find the answer, even if you don't remember it
offhand.  :)

Happy hacking,
t.

Using Math Functions

[calvesmit]

I'm trying to compile the code below, but I can't to do it! gcc always 
complain. 
could someone help me? Why my sistem seems not know about math functions 
althoug i use #include math.h inclusion. 
send any hint to calvesmit@ig.com.br, 'cause I'm not a subscribe of your 
list. 

**********CODE*********** 
#include <stdio.h> 
#include <stdlib.h> 
#include <math.h> 

int main(int argc,char *argv[]) 
{ 
	int i; 
	if(argc==2){ 
		i=atoi(argv[1]); 
		printf("sin(%i)=%0.2f\n",i,sin(i));} 
	return 0; 
} 


**************ERROR MESSAGE************* 
$gcc sin.c -osin 
/root/tmp/ccpbz3XU.o: In function 'main': 
/root/tmp/ccpbz3XU.o(.text+0x32): undefined reference to 'sqrt' 
collect2: ld returned 1 exit status 

_________________________________________________________
Voce quer um iGMail protegido contra vírus e spams? 
Clique aqui: http://www.igmailseguro.ig.com.br