How to break an infinite for(;;) loop in C? - c

Question

I have a vital infinite for loop that allows a sensor to keep updating its values. However I would like to break that for loop when another sensor brings in new values. How can I switch from one infinite for loop to another?
Current code:
for(;;){
SON_Start();
// Wait 65ms for max range time
delay10ms(7);
// Read Range
i = SON_Read(SON_ADDRESSES[sonarReading]);
// pause
delayMs(100);
if(i<15)
drive(200, RadCW);
}
What I would like to add:
If Sensor2 returns a reading (e.g. Sensor2 > 20), then I want to break the loop and goto another infinite for loop to begin a new function.

Answer 1

If you are looking for "switching between 2 infinite loops" it could be "wrapped" by third loop and this "switching" could be done by simple break.
But since you want your program to stop some day, this loop could be placed within the function and you could use return; for ending it:
void myMagicLoop()
{
for(;;)
{
for(;;)
{
if ( I should stop )
return;
if ( I should switch to second loop )
break;
}
for(;;)
{
if ( I should stop )
return;
if ( I should switch back to first loop)
break;
}
}
}
And somewhere you just call:
myMagicLoop();
Hope this helps.

Answer 2

This will switch between loop A and loop B.
for (;;)
{
// Loop A
for (;;)
{
if WANT_TO_SWITCH
{
break;
}
}
// Loop B
for (;;)
{
if WANT_TO_SWITCH
{
break;
}
}
}

Answer 3

You use break; to break a loop and pass control beyond its closing brace. For example
for(;;) {
if( whatever ) {
break;
}
}
//break gets you here

Answer 4

Alternatively you could consider rewriting this with an event-driven approach. This will of course depend on what your hardware is capable of, but at the very least you should be able to produce some timer events.
Then the code would go something like this:
static volatile bool sensor_1_ready;
static volatile bool sensor_2_ready;
for(;;)
{
switch(state_machine)
{
case READING_SENSOR_1:
if(sensor_2_ready)
{
state_machine = READING_SENSOR_2;
}
else if(sensor_1_ready)
{
process sensor 1
}
break;
case READING_SENSOR_2:
if(!sensor_2_ready && some_timeout_etc)
{
state_machine = READING_SENSOR_1;
}
else if(sensor_2_ready)
{
process sensor 2
}
break;
}
}
void callback_sensor_1 (void) // some sort of interrupt or callback function
{
sensor_1_ready = true;
}
void callback_sensor_2 (void) // some sort of interrupt or callback function
{
sensor_2_ready = true;
}
(Before commenting on the volatile variables, please note that volatile is there to prevent dangerous compiler optimizations and not to serve as some mutex guard/atomic access/memory barrier etc.)

Answer 5

The "break" command should do what you need?

Answer 6

The best way to do that is to change the for statement to something like:
for (; Sensor2 <= 20;) {
...
Alternatively you can change it from a for to a while statement:
while (Sensor2 <= 20) {
...
If that doesn't suite your needs you can always use a break instead.

Answer 7

Another option could be to use signals (SIGUSR1,SIGUSR2) to switch from one loop to another.
Something of this sort:
void sensor2(int signum)
{
for (; ;)
...
/* Need to process sensor 1 now */
kill(pid, SIGUSR1);
}
void sensor1(int signum)
{
for (; ;)
...
/* Need to process sensor 2 now */
kill(pid, SIGUSR2);
}
int main()
{
/* register the signal handlers */
signal(SIGUSR1, sensor1);
signal(SIGUSR2, sensor2);
...
}