Request help with conditional compile syntax

Projects Programming
1

I could use some help with the syntax of a conditional compile.

#define SENSOR_NONE    0
#define SENSOR_BMP180  1  // Set to 1 BMP180 Barometric Pressure sensor is installed -- OR
#define SENSOR_HTU21D  2  // set to 2 if HTU21D Temp & Humidity sensor is installed -- OR
#define SENSOR_DS18B20 3  // Set to 3 if DS18B20 Temp sensor is installed on the TinyRTC
#define SENSOR_TYPE SENSOR_HTU21D
                        
#if SENSOR_TYPE == SENSOR_BMP180
	#include <BMP180.h>
	BMP180 weather;
#endif
#if SENSOR_TYPE == SENSOR_HTU21D
	#include <HTU21D.h>
	HTU21D weather;
#endif
#if SENSOR_TYPE == SENSOR_DS18B20
	//TODO: Add code for this sensor
#endif

If the sensor_type is BMP180 (the first one) it compiles. If the sensor_type is HTU21D or DS18B20 I get a ton of compile errors like 'suchAndSuch' was not declared in this scope as if never finds the #endif or like a close brace is missing.
According to some google searches I've done, this should work as I have posted it here, but it doesn't. I've tried a variety of formats including using () and can't seem to find the correct one.

2

It is more likely that it can't find the header files.

3

Yeah probably. It works just fine here (making weather an int and including some random .h as I don't have the ones you're using).

Your problem should be somewhere else, not in the directives.

4

Your problem should be somewhere else, not in the directives.

I suspect that the variable weather is the culprit, because it is not always defined.

OP: You need to study the compiler directives. They have corresponding directives to match if/else if/else. You MUST make sure that weather is ALWAYS defined, because one and only one of the clauses is executed.

5 
#if SENSOR_TYPE == SENSOR_BMP180

The arduino pre-processor can get confused by pre-processor conditional expressions near the start of the file.
Try adding a dummy "real C statement" before any of your conditionals:

static const dummy_c_statement = 0;

#define SENSOR_HTU21D  2  // set to 2 if HTU21D Temp & Humidity sensor is installed -- OR
#define SENSOR_DS18B20 3  // Set to 3 if DS18B20 Temp sensor is installed on the TinyRTC
#define SENSOR_TYPE SENSOR_HTU21D
                        
#if SENSOR_TYPE == SENSOR_BMP180
	#include <BMP180.h>
	BMP180 weather;
#endif