curl / Mailing Lists / curl-library / Single Mail
Buy commercial curl support from WolfSSL. We help you work out your issues, debug your libcurl applications, use the API, port to new platforms, add new features and more. With a team lead by the curl founder himself.

Re: CURLOPT_WRITEFUNCTION issues - warning: curl_easy_setopt expects a curl_write_callback argument

From: Timothe Litt <>
Date: Fri, 21 Jan 2022 06:06:46 -0500

It enables link-time optimizations.  The compiler/linker can see further
into to the source, and detect errors not seen at the module level.

It's saying that your callback routine must be declared/typedefed as a

Timothe Litt
ACM Distinguished Engineer
This communication may not represent the ACM or my employer's views,
if any, on the matters discussed.

On 21-Jan-22 05:11, Gavin Henry via curl-library wrote:
>> -O2 -flto=auto -ffat-lto-objects
>> -fexceptions -g -grecord-gcc-switches -pipe -Wall
>> -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
>> -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
>> -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
>> -m64 -mtune=generic -fasynchronous-unwind-tables
>> -fstack-clash-protection -fcf-protection -Wl,-z,relro -Wl,--as-needed
>> -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld
>> -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1
> So RH is adding about, but it's actually only this that is triggering the error:
> -flto=auto
> Going to read up on what that does which causes:
> error: call to ‘_curl_easy_setopt_err_write_callback’ declared with
> attribute warning: curl_easy_setopt expects a curl_write_callback
> argument for this option [-Werror=attribute-warning]
> 60 | curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION,
> | ^
> lto1: all warnings being treated as errors
> Thanks.

Received on 2022-01-21