On 17/06/2020 11:22, Jakub Wilk wrote:
> * Jonny Grant <jg@xxxxxxxx>, 2020-06-16, 12:36:
>> SYNOPSIS top
>> #define _GNU_SOURCE
>> #include <unistd.h>
>> #include <sys/types.h>
>>
>> pid_t gettid(void);
>>
>> I can compile on Ubuntu without #define _GNU_SOURCE and call gettid()
>>
>> Maybe that line can be removed?
>
> I don't think so. Here's what I get (with GCC 9):
>
> $ gcc test.c
> test.c: In function ‘main’:
> test.c:6:9: warning: implicit declaration of function ‘gettid’; did you mean ‘getgid’? [-Wimplicit-function-declaration]
> 6 | return gettid();
> | ^~~~~~
> | getgid
>
> Prepending "#define _GNU_SOURCE" fixes the above.
Hi Jakub,
Apologies, I should have shared my test case, I was compiling as C++
// g++ -Wall -o tid tid.cpp
#include <unistd.h>
#include <sys/types.h>
int main()
{
return gettid();
}
$ g++ -Wall -o tid tid.cpp
tid.cpp:3: warning: "_GNU_SOURCE" redefined
3 | #define _GNU_SOURCE
|
<command-line>: note: this is the location of the previous definition
Looks like it is set by default, even when specifying the C++ standard version for g++
g++ -std=c++11 -Wall -o tid tid.cpp
Checked, yes, if compiling as C, see the same result as you.
Not sure how it gets enabled by default in my c++
$ g++ --version
g++ (Ubuntu 9.3.0-10ubuntu2) 9.3.0
Cheers, Jonny
