glib defines a number of familiar macros used in many C
programs, shown in Figure 1. All of
these should be self-explanatory.
MIN()/MAX() return the
smaller or larger of their arguments. ABS() returns the absolute value of its
argument. CLAMP(x, low, high)
means x, unless x is outside the range [low, high]; if
x is below the range,
low is returned; if
x is above the range,
high is returned. In addition to the macros
shown in Figure
1, TRUE/FALSE/NULL
are defined as the usual
1/0/((void*)0).
There are also many macros unique to glib, such as the
portable
gpointer-to-gint
and gpointer-to-guint conversions shown in Figure 2.
Most of glib's data structures are designed to store a
gpointer. If you want
to store pointers to dynamically allocated objects,
this is the right thing. However, sometimes you want to
store a simple list of integers without having to
dynamically allocate them. Though the C standard does
not strictly guarantee it, it is possible to store a
gint or guint in a gpointer variable on the wide range
of platforms glib has been ported to; in some cases, an
intermediate cast is required. The macros in Figure 2 abstract the
presence of the cast.
Here's an example:
gint my_int;
gpointer my_pointer;
my_int = 5;
my_pointer = GINT_TO_POINTER(my_int);
printf("We are storing %d\n", GPOINTER_TO_INT(my_pointer));
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Be careful, though; these macros allow you to store an
integer in a pointer, but storing a pointer in an
integer will not work. To do
that portably, you must store the pointer in a long. (It's undoubtedly a bad
idea to do so, however.)
