Use [env] to modify code

PlatformIO IDE
1

Is it possible to make the selected [env] modify code parameters such as variables or pre-processor directives?
I’m thinking how to make say hardware pin definitions change automatically.

2

Aka, build_flags?

3

I thought they were for controlling the compiler, not the source.

4

The compiler can instrumentalize the source.

Consider

; common settings
[env] 
platform = atmelavr
board = uno
framework = arduino

[env:uno_hw_variant_1]
build_flags =
  -D HW_VARIANT_1
  -D BLINK_TIME=500

[env:uno_hw_variant_2]
build_flags =
  -D HW_VARIANT_2
  -D BLINK_TIME=2000

And src/main.cpp

#include <Arduino.h>

#ifdef HW_VARIANT_1
#define LED 13
#elif defined(HW_VARIANT_2)
#define LED 12
#endif

void setup() {pinMode(LED, OUTPUT); }
void loop() { 
  digitalWrite(LED, HIGH);
  delay(BLINK_TIME);
  digitalWrite(LED, LOW);
  delay(BLINK_TIME);
}

Depending on which env you select, it uses a different pinout and blink speed.

5

That’s great. That’s exactly what I was looking for.
Cheers.