pow() function problem

[mazazino]

Hey..im writing a simple application using the pow() function on linux..
the problem is that considering the following code:
int x = 2;
double z = pow(x,2);
this works perfectly fine..compiles and runs normally on both windows and linux..

considering this code however:
int x = 2;
double z = pow(2,x);
this creates an error: "/tmp/ccy3HUjD.o: In function `main':
powers_one.c.text+0x309): undefined reference to `pow'
collect2: ld returned 1 exit status"

BUT IT WORKS ON WINDOWS!...any idea whats the problem?

[Franklin52]

Did you use the -lm compile flag?

Regards

[mazazino]

Did you use the -lm compile flag?

Regards

im kinda new to linux...what do you mean?

[Franklin52]

The standard C library math functions are not included in libc so you have to compile your source with the -lm flag as follow:

gcc powers_one.c -o powers_one -lm

Regards

[mazazino]

The standard C library math functions are not included in libc so you have to compile your source with the -lm flag as follow:

gcc powers_one.c -o powers_one -lm

Regards

ya it worked...thanks..but can u tell me what the -lm does exactly?

[Franklin52]

There are several mathematical functions (e.g. sin, cos, sqrt, exp, log, etc.) provided in the maths library /usr/lib/libm.a.
The math library is separate from the regular C library so you need to explicitly link in the math library, using the -lm flag.

Regards

[Cabhan]

More specifically, "-lSTRING" finds the library that is named STRING and uses the definitions described in it. You need to do this whenever you use a library that is not libc (the standard C library).

So for instance, I was doing some work with Ogg Vorbis files, and I was using some functions defined in libvorbis. Therefore, when I compiled, I had to add "-lvorbis" to the gcc call.

Franklin's explanation explains why you need this for the math functions.