Hello all, everyone's favorite n00b is back with more n0obish questions! This one is actually quite simple, I promise. In short, my C textbook claims that the function "sqrt" is contained within the library math.h so I included it along with stdio.h and stdlib.h in my code. However, whenever I try to use the sqrt function in my code I frequently get the message:

"/tmp/ccG8aDU0.o(.text+0x3d3): In function `GetLen1':
: undefined reference to `sqrt'
collect2: ld returned 1 exit status"

~Note: GetLen1 is the function containing my sqrt line~

Is there something else I am supposed to do before I can use the sqrt command?

Sounds like you need to link with the library containing sqrt (namely math.lib or libmath.a).

I have the line:

"#include <math.h>"

in my code already, specifically how would I write an introduction for those others you have suggested? Would it simply be:

"#include <math.lib>"

?

No, it's going to be some option in your compiler. I would guess from the error that you're using GCC, but do you use the command line or some IDE? On the command line it would be adding an argument to the gcc execution, in an IDE it would depend on the IDE.

I am sorry but I do not understand. When I compile I type:

"cc filename"

into the command line. I don't really know which compiler that is as I am new to the system, but that is it. Do you know how I can debug this program and make it recognize the sqrt function?

The command line to link in the math library is:


The "-lm" is an idiom, telling the compiler to pass information to the linker to use libm.a (the math library).

I would use something like


This lets the compiler give you all of the warnings that it thinks are appropriate for common errors that people make that aren't actually violations of the language but are likely to be mistakes.

Regards,

Dave