cc exited with 256 while using Cairo - gtk

Question

using Cairo ;
using Gtk ;
using GLib ;
public class ClockWidget : DrawingArea {
private Time time ;
private int minute_offset ;
private bool dragging ;
public signal void time_changed (int hour, int minute) ;
public ClockWidget () {
add_events (Gdk.EventMask.BUTTON_PRESS_MASK
| Gdk.EventMask.BUTTON_RELEASE_MASK
| Gdk.EventMask.POINTER_MOTION_MASK);
update () ;
Timeout.add (1000, update) ;
set_size_request (100, 100) ;
}
public override bool draw (Cairo.Context cr) {
int y = get_allocated_height () / 2 ;
int x = get_allocated_width () / 2 ;
var radius = double.min (get_allocated_width () / 2,
get_allocated_height () / 2) - 5 ;
// clock back
cr.arc (x, y, radius, 0, 2 * 3.14) ;
cr.set_source_rgb (1, 1, 1) ;
cr.fill_preserve () ;
cr.set_source_rgb (0, 0, 0) ;
cr.stroke () ;
// clock ticks
for (int i = 0; i < 12; i++) {
int inset ;
cr.save () ;
if (i % 3 == 0) {
inset = (int) (0.2 * radius) ;
} else {
inset = (int) (0.1 * radius) ;
cr.set_line_width (0.5 * cr.get_line_width ()) ;
}
cr.move_to (x + (radius - inset) * Math.cos (i * Math.PI / 6),
y + (radius - inset) * Math.sin (i * Math.PI / 6));
cr.line_to (x + radius * Math.cos (i * Math.PI / 6),
y + radius * Math.sin (i * Math.PI / 6));
cr.stroke ();
cr.restore ();
}
// clock hands
var hours = this.time.hour ;
var minutes = this.time.minute + this.minute_offset ;
var seconds = this.time.second ;
/* hour hand: the hour hand is rotated 30 degrees (pi/6r) per hour + 1/2 a degree (pi/360r) per minute */
cr.save () ;
cr.set_line_width (2.5 * cr.get_line_width ()) ;
cr.move_to (x, y) ;
cr.line_to (x + radius / 2 * Math.sin (Math.PI / 6 * hours
+ Math.PI / 360 * minutes),
y + radius / 2 * -Math.cos (Math.PI / 6 * hours
+ Math.PI / 360 * minutes));
cr.stroke ();
cr.restore ();
// minute hand:
// the minute hand is rotated 6 degrees (pi/30 r) per minute
cr.move_to (x, y);
cr.line_to (x + radius * 0.75 * Math.sin (Math.PI / 30 * minutes),
y + radius * 0.75 * -Math.cos (Math.PI / 30 * minutes));
cr.stroke ();
// seconds hand:
// operates identically to the minute hand
cr.save ();
cr.set_source_rgb (1, 0, 0); // red
cr.move_to (x, y);
cr.line_to (x + radius * 0.7 * Math.sin (Math.PI / 30 * seconds),
y + radius * 0.7 * -Math.cos (Math.PI / 30 * seconds));
cr.stroke ();
cr.restore ();
return false ;
}
public override bool button_press_event (Gdk.EventButton event) {
var minutes = this.time.minute + this.minute_offset;
// From
// http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
var px = event.x - get_allocated_width () / 2;
var py = get_allocated_height () / 2 - event.y;
var lx = Math.sin (Math.PI / 30 * minutes);
var ly = Math.cos (Math.PI / 30 * minutes);
var u = lx * px + ly * py;
// on opposite side of origin
if (u < 0) {
return false;
}
var d2 = Math.pow (px - u * lx, 2) + Math.pow (py - u * ly, 2);
if (d2 < 25) { // 5 pixels away from the line
this.dragging = true;
print ("got minute hand\n");
}
return false;
}
public override bool button_release_event (Gdk.EventButton event) {
if (this.dragging) {
this.dragging = false;
emit_time_changed_signal ((int) event.x, (int) event.y);
}
return false;
}
public override bool motion_notify_event (Gdk.EventMotion event) {
if (this.dragging) {
emit_time_changed_signal ((int) event.x, (int) event.y);
}
return false;
}
private void emit_time_changed_signal (int x, int y) {
// decode the minute hand
// normalise the coordinates around the origin
x -= get_allocated_width () / 2;
y -= get_allocated_height () / 2;
// phi is a bearing from north clockwise, use the same geometry as
// we did to position the minute hand originally
var phi = Math.atan2 (x, -y);
if (phi < 0) {
phi += Math.PI * 2;
}
var hour = this.time.hour;
var minute = (int) (phi * 30 / Math.PI);
// update the offset
this.minute_offset = minute - this.time.minute;
redraw_canvas ();
time_changed (hour, minute);
}
private bool update () {
// update the time
this.time = Time.local (time_t ());
redraw_canvas ();
return true; // keep running this event
}
private void redraw_canvas () {
var window = get_window ();
if (null == window) {
return;
}
var region = window.get_clip_region ();
// redraw the cairo canvas completely by exposing it
window.invalidate_region (region, true);
window.process_updates (true);
}
static int main (string[] args) {
Gtk.init (ref args);
var window = new Window ();
var clock = new ClockWidget ();
window.add (clock);
window.destroy.connect (Gtk.main_quit);
window.show_all ();
Gtk.main ();
return 0;
}
}
How do I solve it??
This is the error displayed:
/usr/bin/ld: /tmp/ccSTGo5z.o: undefined reference to symbol 'pow##GLIBC_2.2.5'
//lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
error: cc exited with status 256
Compilation failed: 1 error(s), 1 warning(s)

Answer 1

You need to link against libm which is the library which provides the pow() function, which you’re using.
Typically this is achieved by passing -lm in your linker flags. I can’t give a more concrete answer because you haven’t said what build system you’re using.

Answer 2

valac -X -lm --pkg gtk+-3.0 clock_widget.vala
I had to compile it with this code.