math.h File seems incomplete

[jayson22]

I am trying to use the sqrt() function that, according to all the help and tutorials I have read, should be included with the #include <math.h> call. This does not seem to be the case as I have tried to compile a bit of source code on two different machines and both of the have failed due to sqrt() being an undefined function. The code snipit looks like this:

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

char input[80];
float ...;
double distSqr, dist;

int main()
{

...

dist = sqrt(distSqr);

...

return(0);
}

My compile line looks like this:

gcc -g -Wall -ansi -pedantic -odist dist.c

And the error I get is:

/tmp/ccY4jY7J.o: In function `main':
/home/.../dist.c:19: undefined reference to `sqrt'
collect2: ld returned 1 exit status

I have browsed the math.h file but I see no reference to the sqrt() function, could someone please help me. I am going to loose it!

Thanks
-Jayson

 

[xwb]

Add -lm to your link line. The math library is called libm.a or libm.so. When linking, drop to lib prefix and the .a/.so/.sl suffix and tell the linker that it is a library with a -l. If the linker can't find it, you have to tell it the directory with a -L

 

[chipperMDW]

It can also be -lmath sometimes, I believe.

Header files just contain declarations for the functions you use in your code. The actual code for most of those functions in is a library called libc, which automatically gets linked in with a typical compile & link.

The math library's code isn't with the regular C code, which is why you have to explicitly link it in.

So you're not going crazy.