Working with GNU/GCC
With this code :
static uint8_t write_idx=0;
write_idx = write_idx==127 ? 0 : ++write_idx;
I get this warning :
warning: operation on 'write_idx' may be undefined [-Wsequence-point]
Do you know what generates this warning ?
EDIT :
write_idx = write_idx==127 ? 0 : write_idx+1;
Same behaviour but no warning thanks @pmg
This can be reduced to:
write_idx = ++write_idx;
The compiler warns because there are two places writing into write_idx without a sequence point. This means the standard does not define what should happen.
Perhaps you don't know that the ++ pre-increment operator modifies the variable and you wanted to write this instead:
write_idx = write_idx==127 ? 0 : write_idx + 1;