[Vm-beginners] Return strings in numeric primitives

[David T. Lewis]

On Sat, Jun 30, 2012 at 12:15:01PM -0300, David Leonhardt wrote:
> Hey.
> 
> I'm doing my own numeric primitive.
> I could return numeric values, doing something like:
> 
>                    self pop: 1 thenPush: ( objectMemory integerObjectOf: 21
> ).
> 
> What I couldn't do is find a way to return a string, for example 'Hello
> World'.


Here is one way to do it. This example is from OSProcessPlugin. If you load
OSProcessPlugin from SqueakSource, you can find a few examples of how this
is used in the primitives.

  stringFromCString: aCString
	"Answer a new String copied from a null-terminated C string.
	Caution: This may invoke the garbage collector."
	| len newString p |
	<var: 'aCString' type: 'const char *'>
	<var: 'p' type: 'void *'>
	len := self
		cCode: 'strlen(aCString)'
		inSmalltalk: [aCString size].
	newString := interpreterProxy
		instantiateClass: interpreterProxy classString
		indexableSize: len.
	p := interpreterProxy arrayValueOf: newString.
	self cCode: 'strncpy(p, aCString, len)'
		inSmalltalk: [ | s |
			s := interpreterProxy firstIndexableField: newString.
			(1 to: len) do: [:i | s at: i - 1 put: (aCString at: i) asciiValue]].
	^ newString


HTH,
Dave