Can i access C #define's in nelua code?

[ghost]

If i do something like this( i know ccinfo.is_winodws exists )

##[[ 
if _WIN32 then 
      -- do some thing
end
]]

is that looking for a variable named as _WIN32 in the nelua pre-processor code?
or
does it also look in the GCC/OS?, so if i don't have a variable named as _WIN32 in the nelua pre-processor code, it will still work because _WIN32 is defined in GCC or in the OS

[edubart]

Is that looking for a variable named as _WIN32 in the nelua pre-processor code?

When you use an if statement in the preprocessor, it will look for a variable in the preprocessor's Lua environment, and _WIN32 is not defined there, unless you define it (by doing _WIN32 = true before the if).

Does it also look in the GCC/OS?

No, the Nelua's preprocessor does not make any define from the C preprocessor visible, but some from the C compiler are converted to values you can find in ccinfo, so you can do if ccinfo.is_windows then to check for Windows, under the hood this will be true in the C compiler also defines _WIN32, and it's an effective way to detect windows.

Can I access C #define's in Nelua code?

I'm going to explain the current ways to do this below.

1. Using ccinfo (recommended)

This is the recommended way to use values present in ccinfo. The variable ccinfo is a table containing information about the target features and C compiler features, you should use it to detect different OS, architectures, C compilers.

-- Using ccinfo (recommended)
## if ccinfo.is_win32 then
  print 'target is win32'
## end

2. Injecting C #ifdef (not recommended)

Injecting C ifdefs is also possible, this can be useful if you want to generate portable C code, by portable I mean a C code that can be compiled in different systems. However this approach is not recommended, because this will not work with some language features, like defer and <close> variables, because this hides the control flow from the Nelua compiler.

-- Injecting C ifdefs (not recommended)
## cemit '#ifdef _WIN32'
  print 'target is win32'
## cemit '#endif'

3. Parsing C defines using the C compiler

Nelua has a utility to parse C defines from any C header into a table containing all visible C defines. I don't encourage doing this because it will slowdown compilation due to extra process executions, and the table may contain values you would not expect compiling with a different C compiler or target.

-- Parsing C defines with your C compiler
## local ccdefs = require'nelua.ccompiler'.get_cc_defines('<windows.h>')
## if ccdefs._WIN32 then
  print 'target is win32'
  print('WINVER ', #[ccdefs.WINVER]#)
  print('_WIN32_WINNT', #[ccdefs._WIN32_WINNT]#)
## end

4. Setting defines manually

You can define preprocessor variables manually, this is the most simple, but requires user configuration, defines can also be passed with command line arguments, for example with nelua -DPLATFORM_WINDOWS myprog.lua.

-- Setting your define manually
## PLATFORM_WINDOWS = true
## if PLATFORM_WINDOWS then
  print 'target is windows platform!'
## end

[ghost]

Okay, Thank you so much 👍