I strongly advise against using either since both are not only non-portable, but also break any compiler support for getting you warnings when you're using it w

I strongly advise against using either since both are not only non-portable, but also break any compiler support for getting you warnings when you're using it wrong. The Linux kernel style suffix extensions (cf. https://www.kernel.org/doc/Documentation/printk-formats.txt https://www.kernel.org/doc/Documentation/printk-formats.txt) are much better on the latter front.