Passing a pointer to a pointer in Smalltalk

In Smalltalk, you can pass a pointer created in C or COBOL to a Smalltalk pointer. Consider the following record definition:

void pointerToPointerToChar ( char ** ppChar );

The code below can be used to call the above function:

| func1 pChar ppChar theString |

func1 := PlatformFunction callingConvention: 'c'

function: 'pointerToPointerToChar'

library: 'mylib'

parameterTypes: #(pointer)

returnType: #none.

"Create a pointer to a String. Memory must be freed when finished"

theString := 'String to be passed'.

pChar := theString copyToOSMemory.

"Create a ByteArray to store the address of pChar. Passing a ByteArray

to a PlatformFunction expecting parameter with type 'pointer' will

result in a pointer to the ByteArray being passed to the external function"

ppChar := ( ByteArray new: 4 ) uint32At: 0 put: pChar asInteger.

func1 callWith: ppChar abtAsExternalPassedPointer.

"Extract the null-terminated string from the pointer address"

theString := pChar abrAsString.

"Free the memory allocated for pChar"

pChar free.

Last modified date: 01/29/2015