int main()
{
int current_errno = errno;
printf("errno: %d\n", current_errno);
return 0;
}
```
and `cpp errno.c` tells me at the end
```ada
# 4 "errno.c"
int main()
{
int current_errno =
# 6 "errno.c" 3 4
(*__error())
# 6 "errno.c"
;
printf("errno: %d\n", current_errno);
return 0;
}
```
so, _on a Mac_, `errno` is in fact a function call to whatever `__error` is pointing to (or maybe, my C isn’t that great, `__error()` returns a pointer to the appropriate actual `errno`? otherwise, how could you say e.g. `errno = EINVAL;` ?).
For portability, you’d have to write a C function to pick up `errno` and return that, and then import that function.
---
### Author:  [@dmitry-kazakov](https://forum.ada-lang.io/u/dmitry-kazakov)
#### Post date: [November 20, 2024, 8:21am UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/4 "2024-11-20T08:21:12Z")
First of all it is int.
Second, a along story, but its short version is that you cannot link to an object. Linux provides a function that returns the address of errno. Use it:
```ada
function errno return int is
function errno_location return access int;
pragma Import (C, errno_location, "__errno_location");
begin
return errno_location.all;
end errno;
```
---
### Author:  [@Fabien.C](https://forum.ada-lang.io/u/Fabien.C)
#### Post date: [November 20, 2024, 5:17pm UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/5 "2024-11-20T17:17:15Z")
> [@nerd\_type](#):
>
> I there a good way to read ‘errno’ in Ada?
Use `GNAT.OS_Lib.Errno` and `GNAT.OSLib.Errno_Message`:
```ada
function Errno return Integer;
function Errno_Message
(Err : Integer := Errno;
Default : String := "") return String;
-- Return a message describing the given Errno value. If none is provided
-- by the system, return Default if not empty, else return a generic
-- message indicating the numeric errno value.
```
---
### Author:  [@nerd\_type](https://forum.ada-lang.io/u/nerd_type)
#### Post date: [November 20, 2024, 5:26pm UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/6 "2024-11-20T17:26:52Z")
Thanks for the replies guys!
---
### Author:  [@mosteo](https://forum.ada-lang.io/u/mosteo)
#### Post date: [November 22, 2024, 12:46pm UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/7 "2024-11-22T12:46:24Z")
In this case Fabien’s is the simplest, but for the general C case what I do in these cases is to have a simple wrapper function in C that calls whatever complex magic/macro/C++ element is there, so I can safely bind to my C wrapper.
---
### Author:  [@mgrojo](https://forum.ada-lang.io/u/mgrojo)
#### Post date: [November 22, 2024, 5:58pm UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/8 "2024-11-22T17:58:56Z")
It would be nice to have a tool that detects those macros and generates those simple wrapper functions. That could complement `gcc -fdump-ada-spec` for easily generating bindings to C libraries. In fact, I don’t know why `gcc` couldn’t do that by itself.
---
### Author:  [@pyj](https://forum.ada-lang.io/u/pyj)
#### Post date: [November 23, 2024, 3:11am UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/9 "2024-11-23T03:11:07Z")
Per [cppreference](https://en.cppreference.com/w/c/error), errno is:
> macro which expands to POSIX-compatible thread-local error number variable
The `errno` in `libc.so.6` here is in thread local storage (TLS):
> [@nerd\_type](#):
>
> ```ada
> /usr/bin/ld: errno: TLS definition in /lib/x86_64-linux-gnu/libc.so.6 section .tbss
>
> ```
and your import attempts to find a non-thread local storage version:
> [@nerd\_type](#):
>
> ```ada
> mismatches non-TLS reference in ./test_ioctl.o
>
> ```
---
### Author:  [@Blady](https://forum.ada-lang.io/u/Blady)
#### Post date: [November 24, 2024, 10:34am UTC](https://forum.ada-lang.io/t/using-errno-with-ada/1490/10 "2024-11-24T10:34:11Z")
You may also consider POSIX Ada with [Florist](https://github.com/Blady-Com/florist):
function Get\_Error\_Code return Error\_Code;
(in generated posix.ads)