whats the -lm do ? info was just to overwhelming

12-28-2001, 12:07 PM

Just would like to now what the gcc option -lm means/does

I got into trouble using the sin function from math.h and found a message on the board from someone with the same problem.

The answer suggested to use the -lm which also works for me.
Ofcourse I would like to know now what it does. The info pages are just to overwhelming with info for a newbie like me.

Engineer · 12-28-2001, 07:25 PM

the -lm option tells gcc to link (that's what the 'l' stands for) your code with the "math" (this what the math library is called) shared library. It's almost like DLL's in windows...

12-29-2001, 03:49 AM

Ok, thanks but that gives me another question. I do not have to to use a parameter like -ls for linking the stdio so why do i have to do this for the math and not for stdio ?

I thought they were both standard functions of ANSI-C ?

alex · 12-29-2001, 06:21 AM

Hi!

All non-mathematical ANSI-C functions are stored in libc.a/libc.so, which is always included automatically by gcc, the mathematical ANSI-C functions are stored in libm.a/libm.so, which is available if you install gcc, but is not automagically included like the MS and Borland compiler. Those compilers try to guess whether the math library is needed... The Borland compiler used to get it wrong sometimes, which they fixed in the newest version. The MS compiles used to get it right, but the latest MS compilers have this problem:

Code:

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

main()
{
   printf("%e\n", 1.0);
}

The MS compiler compiles this without a problem, but it gives runtime errors! (the math library is needed to convert the second argument into a string, but it is erroneously not linked to the binary)

alex

12-30-2001, 04:12 AM

Thanks! Thats the stuff I want to know

12-28-2001, 12:07 PM	#1
oeleboele Guest Posts: n/a	whats the -lm do ? info was just to overwhelming Just would like to now what the gcc option -lm means/does I got into trouble using the sin function from math.h and found a message on the board from someone with the same problem. The answer suggested to use the -lm which also works for me. Ofcourse I would like to know now what it does. The info pages are just to overwhelming with info for a newbie like me.

12-28-2001, 07:25 PM	#2
Engineer Registered User Join Date: Oct 2001 Posts: 125	the -lm option tells gcc to link (that's what the 'l' stands for) your code with the "math" (this what the math library is called) shared library. It's almost like DLL's in windows... __________________ 1 rule of the Samurai Code: if you have nothing to say, don't say anything at all!
Engineer is offline

12-29-2001, 06:21 AM	#4
alex Registered User Join Date: Sep 2001 Posts: 132	Hi! All non-mathematical ANSI-C functions are stored in libc.a/libc.so, which is always included automatically by gcc, the mathematical ANSI-C functions are stored in libm.a/libm.so, which is available if you install gcc, but is not automagically included like the MS and Borland compiler. Those compilers try to guess whether the math library is needed... The Borland compiler used to get it wrong sometimes, which they fixed in the newest version. The MS compiles used to get it right, but the latest MS compilers have this problem: Code: #include <stdio.h> #include <math.h> main() { printf("%e\n", 1.0); } The MS compiler compiles this without a problem, but it gives runtime errors! (the math library is needed to convert the second argument into a string, but it is erroneously not linked to the binary) alex
alex is offline

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12-29-2001, 03:49 AM	#3
oeleboele Guest Posts: n/a	Ok, thanks but that gives me another question. I do not have to to use a parameter like -ls for linking the stdio so why do i have to do this for the math and not for stdio ? I thought they were both standard functions of ANSI-C ?

12-30-2001, 04:12 AM	#5
oeleboele Guest Posts: n/a	Thanks! Thats the stuff I want to know