quadmath and argument type for scanf

I use the <quadmath.h>. With which argument type can I read my input correctly? If I use double it looks like:

printf("enter 3 values for s, t and mt:\n");
scanf("%lf %lf %lf", &s, &t, &mt);
printf("%lf %lf %lf\n", s, t, mt);

I tried different possibilities instead of "l" for example:

scanf("%Qf %Qf %Qf", &s, &t, &mt);

or even without

 scanf("%f %f %f", &s, &t, &mt);

however I get an error.

scanf (and related functions and printf and related functions) is not extensible. It can only parse what the standard library knows about. The C standard library comes with the operating system, not the compiler. It does not know about libquadmath, which is a compiler extension.

So you'll have to read strings and convert them separately using strtoflt128.

Note that C++ streams can be extended to extract __float128, but I don't see C++ interface in the quadmath library.