预处理器宏问题

Question

I wanted to write a debug log print function for my finite state machine that prints the current state, the time in milliseconds and then my message. However, I get random results. This is what I did:

#define DEBUG_PRINT(tag, format, ...) printf("[%10s] %7d: " format "\n", tag, millis(), ##__VA_ARGS__)

When I run:

DEBUG_PRINT("SETUP", "%d %d %d %d", 1, 2, 3, 4);

I expect to get: [ SETUP] 0: 1 2 3 4
But I get: [ SETUP] 0: 0 1 2 3

Adding an extra %d will get the "4", but I still get an spurious 0.

My previous debut log macro: DEBUG_PRINT1("%d %d %d %d", 1, 2, 3, 4); prints the expected 1 2 3 4 .

Can you help me to get rid of that extra 0?

Answer 1

The problem is that the millis() function returns an unsigned long , where as the identifier is a %d integer.

Change it to %7ld and it should work fine.

I have tested it.

edit 1:

I have also tested it on a linux system. In the linux system this is not a problem there because the size of a linux int is 4 bytes and long is 8 bytes.

On the Arduino however, the size of an int is 2 bytes and long is 4 bytes. This screws up the %d identifier on the Arduino, and extends the unsigned long from millis() to the next %d