AVR Freaks

You missed this

 

You missed the "as part of the usual arithmetic conversions" part. The "+, -, and ~" are referring to the unary operators. So addition, subtraction, multiplication, and division all invoke integer promotion.

 

"Usual arithmetic conversions" is defined in 6.3.1.8.

There's a reason that "people who can interpret Language Standards Documents and come up with either "your code is wrong" or "the compiler is wrong"" get put into a separate class.  Sometimes highly valued. sometimes cursed at (frequently both.)

 

 :-)

 

C++ has more ways for a clueless programmer to write bad code, I suppose.  It also has ways for programmers to write better code.  The advantages of C++ increase as the complexity of the program increases. 

 

I just ran an experiment.  I found a simple C program on this site that blinks a LED.  It's all written in main.  I converted it to C++ and the resulting machine code is almost identical. The C++ program uses one more program memory byte than the C program.  The .hex files are identical except for the last 4 lines.

 

// C code

// #define F_CPU 2000000
#define F_CPU 2000    // for simulator cuz it's 1000 times slower.

#include <avr/io.h>
#include <util/delay.h>

#define BLINK_DELAY_MS 1000

 

int main(void)
{
PORTC.DIRSET = 0b10000000 ; // Set pin 7 to be output.

while(1){ // loop forever
    PORTC.OUTSET = 0b10000000 ; // set the output high.
    _delay_ms( BLINK_DELAY_MS ) ; // wait.
    PORTC.OUTCLR = 0b10000000 ; // set the output low.
    _delay_ms( BLINK_DELAY_MS ) ; // wait.
    }
}

 

 

// C++ code

// #define F_CPU 2000000
   #define F_CPU 2000   // for simulator because it's 1000 times slower

#include <util/delay.h>
#include "port_c_device.h"

#define BLINK_DELAY_MS 1000

 

int main(void)
{
(new Port_c_device)->Set_pins_direction_out(Port_device::Pin7);

while(1)  { // loop forever
    (new Port_c_device)->Set_out_pins_high(Port_device::Pin7);
    _delay_ms( BLINK_DELAY_MS ) ; // wait.
    (new Port_c_device)->Set_out_pins_low(Port_device::Pin7);
    _delay_ms( BLINK_DELAY_MS ) ; // wait.
    }
}