It is 4 spaces, no tabs, preferrably at 80 columns per line. The preferred coding style is explained by example. Source file example: /* Copyright LICENSE TEXT */ #include "foo.h" #include "bar.h" #include <glib.h> void foobar (FooEnum bar, const gchar* foo) { gint n, i; if (!foo) return; #ifdef BAR_STRICT if (bar == FOO_N) { g_print ("illegal value for 'bar'.\n"); return; } #endif /* this is an example */ switch (bar) { case FOO_FOO: n = bar + 1; break; case FOO_BAR: n = bar + 10; break; default: n = 1; } for (i = 0; i < n; i++) { g_print ("%s\n", foo); } } Header file example: /* Copyright LICENSE TEXT */ #ifndef __FOO_H__ #define __FOO_H__ 1 #ifdef HAVE_BAR_H #define BAR_STRICT #endif /* Types */ typedef enum { FOO_FOO, FOO_BAR, FOO_N } FooEnum; typedef struct { FooEnum foo_bar; } FooStruct; /* Declarations */ void foo_bar (FooEnum bar, const gchar* foo); const gchar* foo_foo (FooStruct foo_struct, guint number, gboolean flag); #endif /* !__FOO_H__ */