Problem with sqrt function

[StriderV]

I have 2 integer variables which I want to multiply then find the square root (the geometric mean). This result needs to be saved in a double variable.

I have tried typecasting them, but something about my function isn't working right. I always get this error

Undefined                       first referenced
 symbol                             in file
sqrt                                /tmpsort/ccAKaa8v.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

At first I thought I was typecasting wrong, but when I removed all of that and simply tried to do sqrt on a single double variable, I still hit the error.

double d, e;

d = 3.2;
e = sqrt(d);

I don't get the error if I do sqrt on a number.

double e;
e = sqrt(3.2);

I have included math.h.

[kjerosky]

What compiler are you using? I know that when I compile with GCC, I have to include the -lm flag to include the math library, like so:

gcc myprog.c -o myprog -lm

-Keith

[StriderV]

What compiler are you using? I know that when I compile with GCC, I have to include the -lm flag to include the math library, like so:

gcc myprog.c -o myprog -lm

-Keith

Thank you, this worked..

That's pretty annoying that I'll have to include that tag everytime I compile something that uses math.h though. I might just write my own sqrt function

Do you know if this is the case for any other library? And why is math.h like this?

[kjerosky]

No problem - I do this to myself every so often, and I've been programming for a long time. :P I can't think of many other times where I've had to use the -l flag to include standard C libraries besides the math one, though when I create my own libraries I definitely have to use it. Here's a nice link to why math.h requires the -lm flag: compile - Why do you have to link the math library in C? - Stack Overflow

Good luck!

-Keith

[tabstop]

The only library that is automatically linked by default is the C runtime (which contains everything in the standard C libraries and then some); all the rest require -l.

Historically, the math library was kept separate so that people could choose between "fast" and "accurate" back when it wasn't possible to do both at the same time. However, I haven't been on a system where I've needed to use -lm for a while, and I don't know that I'm doing anything special. Presumably that means that whoever installed/set up your system doesn't like you. (Okay, maybe that's not the reason.)

(EDIT: No wait, I do for things like sqrt. I had forgotten which things, and looked at the wrong source. Sorry.)