Scope of pre-compiler directives.

Projects Programming
1

What's the scope of a pre-compiler directive? Is it global?

Here's the background. I've written a number of libraries that all use the same library to write to a log file on an SD card. I need to be able to switch between using one of two different (but very similar) libraries to write this file.

My top level sketch includes this pre-compiler directive and conditional statement....

#define LOG3                               // Switches between using the singleton logger <Log3.h> or <log3.h>

#ifdef LOG3                                   // Switches between using the singleton logger based on <Log3.h> or <log3.h>
#include <Log3.h>                             // Logger (opens, writes one line & closes the file)
#else
#include <Log2.h>                             // Logger (opens the log file and leaves it open all the time)
#endif

#include <SingLog2.h>                      // Singleton version of the log file

So if I define LOG3 then the code should use my log3.h library, if I don't define it I should use log2.h

And the code for the logger itself (SingLog2.cpp) includes the following....

#ifdef LOG3
static Log3 logFile;             // Version 3 of the log file library
#else
static Log2 logFile;             // Version 2 of the log file library
#endif

I thought that the scope of the pre-compiler directive was supposed to be global, but experimentation indicates that isn't the case.

If the pre-compiler isn't global, is there anyway to achieve what I'm trying to do? If I can't add a global switch then every time I switch between arduino projects I'm going to have manually edit every library, and then edit them back again next time I change projects again.

Thanks

2

If I can't add a global switch then every time I switch between arduino projects I'm going to have manually edit every library, and then edit them back again next time I change projects again.

Or put the library files in the same folder as the sketch and #include them using quote marks around the .h filename.

3

Hello,

It looks like this known bug, which was apparently fixed. So try with latest version of the Arduino IDE.

4

It looks like this known bug, which was apparently fixed

Ok thanks, so it ought to work and isn't a cock up on my part for once! I'll try upgrading

5

apparently fixed

Where did you find information that this was fixed?

I've just upgraded to 1.6.5 and still have the same error. I can't find any mention of it being fixed in any release notes.

6

Or put the library files in the same folder as the sketch and #include them using quote marks around the .h filename.

I would prefer NOT to do this, the libraries get used by multiple projects so I'd need to make multiple copies, one for each project - a configuration nightmare

7

I understand why you would not want to do it that way, but it is an option.

I need to be able to switch between using one of two different (but very similar) libraries to write this file.

Why not have a single library that is initialised from the main program with different parameters to provide different functionality ?

8

Why not have a single library that is initialised from the main program with different parameters to provide different functionality ?

That's a possibility, but this particular library is used for general logging so it's used by ALL the libraries I use. Adding an extra parameter to switch functionality would require making changes (albeit minor) to every library I use (that's probably over a hundred libraries!)

Being able to switch between libraries at the top-level sketch would make things a whole lot easier.

9

What you are doing involves editing the sketch itself anyway so why not edit the #include directly?