How to link specific C language headers

General
1

Hello, this is my first topic on this forum. I’m having issues getting a test program to compile. Here’s the relevant code:
http://verisimilitudes.net/2023-09-30

I’ve never had to fiddle with compiler options, because I only use the C language standard library, but I’ve been unable to get this test to compile; I’m always told that sqrt is undefined. I’m not at all certain as to what I’m doing wrong here, but I’d appreciate any direction.

2

Someone who knows better will likely respond, but: looking at the ARM, I don’t see a Sqrt function defined in Interfaces.C or any other package you are useing. Do you have some other idea where it should be defined?

I suspect that if you want access to the C standard library’s sqrt function, then you’ll need to create the bindings, unless they already exist somewhere.

3

Yes, I’m trying to use the C standard library’s sqrt function, but I can’t get it to link for some reason, and I’ve never had this issue before.

4

Assuming this is on a POSIX-ish environment, you need to add -lm to your linker switches to get the math functions from libm.

If you’re using gprbuild, try adding this to your .gpr file:

package Linker is
    for Switches ("Ada") use ("-lm");
end Linker;

Here’s my version using the gnatmake flags -largs -lm:

5

This is very odd, then, as I already found and used those flags, to no success.

6

On macOS,

  • the function for errno is __error()
  • the linker finds _sqrt without special switches
  • sqrt(-1.0) sets errno to 0 (or, leaves it at 0)
  • the result of sqrt(-1.0) is NaN
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