For construct with pointers [SOLVED]

Projects Programming
1

Hi,

In Nick Gammon's forum, I read about SPI. There is a for( ; ; ) construct that uses pointers.

for (const char * p = "Fab" ; c = *p; p++)
    SPI.transfer (c);

for (const char * p = "Hello, world!\n" ; c = *p; p++)
  SPI.transfer (c);

The initialisation part sets a pointer to a string (no null termination).

The continue for clause part: c = *p is the part that I don't understand

The last part just advances the pointer as expected.

Can anyone shed some light on this for me?

Thanks all.

Jacques

2

All hardcoded strings include the null at the end. That's why char strConst[]="abc"; has 4 characters in memory. The value of the null is zero. What is the internal representation of FALSE?

Remember an assignment (single =) is an expression which returns a value. The value which is assigned.

a = b = c; will give both a and b the value of c.

:wink:

3

The initialization does have null termination, it's a string in quotes!

c=*p sets c to the current value pointed to by p - and that value is interpreted as true or false for purposes of whether the loop keeps going. As long as c is not 0, that's true and the loop keeps going. When it hits the null terminator, c gets set to 0, which is false, so the loop ends at that point.

4

I forgot about the null character being automatically appended to hard coded strings. I must have read that line in the reference page half a dozen times...

Thanks Morgan.

EDIT: And you too DrAzzy