Declaring fixed-size strings.

[TurkeyLurkerParticipant]

In C, I could allocate a data buffer as follows:

char buffer[256]

How would I do this in Monkey2? I don’t mind if the GC annihilates the string after the function call. I just want a string with a max size of 256 bytes required by an api call from an external library. Right now I am spacing out 200 characters within quotes to preallocate the string; does the job, but isn’t very um… cerebral.

[TurkeyLurkerParticipant]

Ok, after more thought, I’ve come up with this:

Monkey

[crayon-5cba95336e59f221130232 inline="true" ]Local myStr:String = String.FromChars(New Int[256]) myStr = get_library_path(myStr)

1 2	[crayon-5cba95336e59f221130232 inline="true" ]Local myStr:String = String.FromChars(New Int[256]) myStr = get_library_path(myStr)

[/crayon]

This “appears” to work when compiled and ran, but is it a safe call to make?

[abakoboParticipant]

you have the databuffer, wich you can find in some of the mx2 source.

Here’s some code I used in the past. It’s not fixed size but well you can just put a constant instead of ‘str.CStringLength’..
Now I learn that Strings can be implicitly converted to Cstrings so I won’t use it anymore but if you need fixed size It may be what you need.. If you method looks to not work so well finaly.

Local mydata:=New DataBuffer( str.CStringLength ) ‘the length is in Bytes!
str.ToCString( mydata.Data,mydata.Length )

[TurkeyLurkerParticipant]

Thanks abakobo.

[Mark SiblyKeymaster]

I recommend using a libc.char_t pointer if you need to provide a fixed sized string or string buffer. A CString may not work, as CStrings should not be modified and are subtly different.

For example, here’s roughly how monkey2 CurrentDir function wraps the libc getcwd call:

Monkey

#Import "<libc>" extern Function getcwd:libc.char_t Ptr( buf:libc.char_t Ptr,size:Int ) public Function CurrentDir:String() Local buf:=New char_t[PATH_MAX] getcwd( buf.Data,PATH_MAX ) Local path:=String.FromCString( buf.Data ) Return path End

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

#Import "<libc>"   extern   Function getcwd:libc.char_t Ptr( buf:libc.char_t Ptr,size:Int )   public   Function CurrentDir:String() Local buf:=New char_t[PATH_MAX] getcwd( buf.Data,PATH_MAX ) Local path:=String.FromCString( buf.Data )   Return path End

Not pretty, but that’s c/c++ strings for you. I recommend wrapping ‘messy’ calls like this instead of using them directly, as above.

I also recommend looking at the libc module and std filesystem for ideas on how to write C API wrappers.

[TurkeyLurkerParticipant]

Thanks Mark. I’ve ported the library code to use char_t on your advice. It does mess up the code a bit, but a class I am writing already wraps the library anyway so all is well.

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