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Description
In Arduino.h header file, there are these macro
#define min(a,b) ((a)<(b)?(a):(b))
#define max(a,b) ((a)>(b)?(a):(b))
#define abs(x) ((x)>0?(x):-(x))
#define constrain(amt,low,high) ((amt)<(low)?(low):((amt)>(high)?(high):(amt)))
#define round(x) ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))
#define sq(x) ((x)*(x))
When using these macros with function calls, the function get called twice (or multiple times), which cause potential bug (when function return different value)
Simple test program which show this bug
#include <Arduino.h>
void setup() {
Serial.begin(9600);
}
void loop() {
for (int i = 0; i < 20; i++) {
Serial.println(max(rand() % 10, 5));
}
while (true) {
// stop
}
}
Reference: https://www.youtube.com/watch?v=j0_u26Vpb4w&t=632s
Activity
per1234 commentedon Mar 29, 2020
Note that, as discussed at arduino/ArduinoCore-API#85, this issue has already been resolved for
min
andmax
inarduino/ArduinoCore-API
:https://github.com/arduino/ArduinoCore-API/blob/82a5055a0588976c8df8c1ff3d978f62d68410f3/api/Common.h#L124-L149
So it would be partially resolved by migrating this core to using ArduinoCore-API (#329)
The Arduino Language Reference does warn about this problem: arduino/reference-en#513