On Sun, 26.10.14 07:51, Martin Pitt (martin.p...@ubuntu.com) wrote: > > > +static const char hwdb_bin_paths[] = > > > + "/etc/udev/hwdb.bin\0" > > > + UDEVLIBEXECDIR "/hwdb.bin\0"; > > Actually we don't need to define a variable for this, a #define would be > > enough. > > Are #defines actually preferred in systemd's code style/conventions? > Personally I prefer "proper" constants, as they are more type safe and > less magic, and presumably string constants will end up in the same > place in the ELF anyway? Using #defines potentially duplicates the > strings too, although I suspect gcc to be clever enough to > de-duplicate identical string constants in the source. Is there any > downside to using static constants?
Well, there's quite a difference between string macros and string constants. In C string macros are usually preferable, since they allow compilers to arrange things pretty freely, as they do not imply the actual allocation of a variable in the ELF result for this. Moreover, string macros have the benefit that you can use them to put together strings at build time, the way you do it above even. Currently, in systemd we try to be conservative: a) Paths that are not really configurable aren't really made configurable, and hence are hardcoded as literal strings (such as the "/etc/udev" above...) Given that systemd is pretty much at the core of the OS very little of systemd is relocatable, which in turn means that most of its own paths are actually not configurable. In fact we should probably refuse building if people try to build systemd with prefix=/waldo... b) For configurable and non-obvious strings we use string macros b) Complex strings, for example NULSTR-style things, that "feel" more like an array than a real string are placed in string constants. That alls said, the lines are blurry and we don't follow these rules strictly so far... Hope that makes sense? Lennart -- Lennart Poettering, Red Hat _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
