Calculate the abs value of a complex in C

Question

Part of the source code:

double _Complex z = 1.0 + 1.0*I;
printf("%f\n", cabs(z));

My development environment: Ubuntu16.04LTS, Clion IDE with GCC version 5.4.0, C11 standard.

As I run the code, an error occurs with message

undefined reference to `cabs'

The IDE tells me that the function cabs is declared in the header file cmathcalls.h, so I try to:

#include<cmathcalls.h>

But the IDE warns me that the file cannot be found, so again I try:

#include<bits/cmathcalls>

The I run the code, however it still doesn't work.

I want to know how can I get the abs value of the complex z with the function cabs?

You write: _"As I run the code..."_. Do you rather mean _"when I compile the code..."_? — Jabberwocky, Feb 07 '18 at 09:23
You should really have a closer look on the messages of compiler, linker etc. that your IDE hopefully displays somewhere. Here you can see *what exactly* fails. Simply hitting [Run] sometimes includes a build of the program. — Wolf, Feb 07 '18 at 09:29
did you add the library to `CMakeLists.txt`? `target_link_libraries( m)` — uta, Feb 20 '18 at 14:16

score 6 · Accepted Answer · answered Feb 07 '18 at 09:06

6

For cabs you just need <complex.h>. Where it is actually declared is just an implementation detail.

And then link with -lm to actually link the math library in.

answered Feb 07 '18 at 09:06

1

I use the command line to compile my code,with '-lm'added,it works.But can I make it work using the IDE? – 罗通侯君 Feb 07 '18 at 09:24
1

@罗通侯君 - Follow the instructions [here](https://stackoverflow.com/questions/39150697/build-and-run-project-that-use-math-h-in-clion). – StoryTeller - Unslander Monica Feb 07 '18 at 09:27

1 Answers1