Brian Dessent schrieb: > Florian Gleixner wrote: > >> gcc r.c -lm >> r.c: In function 'main': >> r.c:9: warning: incompatible implicit declaration of built-in function >> 'round' > > I'm assuming that your C library is glibc, i.e. you're using Linux. It > is always a good idea to state what platform you are using, because gcc > supports many dozens of platforms so don't assume we know what you're > using. > Good guess. I will be more verbose next time. > The problem you are seeing is that glibc has a number of feature levels > that it supports. By default, it only exposes a fraction of available > features (C90) in its headers. You have to explicitly define the level > of feature support that you want: > <http://www.gnu.org/software/libc/manual/html_node/Feature-Test-Macros.html>. > Defining _GNU_SOURCE gets you everything and is the most commonly used, > e.g. by adding -D_GNU_SOURCE to CFLAGS. I think that if you use > autoconf, it takes care of this for you if it detects you're on a glibc > system, but I could be wrong. Autoconf did not help me here automatically. But maybe i have to change something in configure.ac? So what is the "right way"? Use -D_GNU_SOURCE while compiling or add a #define? I decided to add the #define, and it works. Thank you for your explanation and help! Flo
