String.ToCString() issues

[jondecker76Participant]

First, I’ve found a bug in the implementation in modules/monkey/types.monkey2 line 217.  ToCString should take two parameters, not one – as defined in the native .cpp file (I already submitted the bug report and fixed it/rebuild modules here locally)

 

However, I still can’t get it to work as expected and I get hit with a memory access violation.

Here is what I am trying to do:

I’m using an extern to a .c source file, which contains:

Monkey

char *dev_name = "/dev/video0";

1	char *dev_name   = "/dev/video0";

This is externed in my .monkey2 file as:

Monkey

Extern Global dev_name:UByte Ptr

1 2	Extern Global dev_name:UByte Ptr

Then, I try to use it and it bombs out:

Monkey

local dev:="/device/video0" dev.ToCString(dev_name,dev.Length)

1 2 3

local dev:="/device/video0"   dev.ToCString(dev_name,dev.Length)

any ideas?  Has anyone else used ToCString() yet?

[DaniloParticipant]

Should it be?

Monkey

[crayon-5cb9ba0aed6b0636433524 inline="true" ]Extern Global dev_name:CString

1 2	[crayon-5cb9ba0aed6b0636433524 inline="true" ]Extern Global dev_name:CString

[/crayon]

Docs say monkey.types.CString is the mapping for “char *”

[Mark SiblyKeymaster]

> char *dev_name   = “/dev/video0”;

Literal c/c++ strings like this are stored in ‘read only’ memory and shouldn’t be written to.

Try this instead…

char dev_name[256];

dev_name will intially be ’empty’ but that’s OK because you’re using ToCString to initialize it before you use it (I hope).

The alternative is to pass the dev_name directly to native code, eg:

Monkey

//c++ void open_dev( const char *name ){ } ' mx2 Extern Function open_dev( name:CString )

1 2 3 4 5 6 7 8 9 10 11 12

//c++   void open_dev( const char *name ){ }   ' mx2   Extern   Function open_dev( name:CString )

This will automagically convert name to a const char * for you when you call open_dev. However, you should NOT store ‘name’ anywhere inside open_dev for later use as the const char * is temporary and will disappear after open_dev returns.

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