On 29 Nov 2021, at 10:10, Guillermo Polito <guillermopolito@gmail.com> wrote:
Hi Gerry,
I think the point of Tomaz is that an FFI method can only have a single #ffiCall: statement. In your example, what you can do is to split your method in two methods:
First a method with the mapping (following the idea of Tomaz but using libc)
FFITutorial>>getHostNameInto: hostName ofLenght: length
^self ffiCall: #( int gethostname(char *hostName, int length) ) library: 'libc.so.6'.
And then have a second method that calls this one:
FFITutorial>>getHostName
| nameBuffer |
nameBuffer := ByteArray new: 256.
self getHostNameInto: nameBuffer ofLenght: 256.
^nameBuffer asString
Notice that converting the byte array buffer to string will only work by chance if the called function returns characters encoded in ascii. In Pharo strings are Unicode characters where each character is a unicode code-point.
In general #utf8Decoded is better than #asString since UTF-8 includes 7-bit ASCII. It will fail when the native encoding is one of the simpler byte encodings, like Latin1 (or iso-8859-1), though.
The best thing is to read the documentation of the library and check the encoding of the string that is put in the buffer to decode it accordingly, for example from utf8.
G
El 29 nov 2021, a las 0:56, Gerry Weaver <gerryw@compvia.com> escribió:
Hi,
Thanks for the example. Unfortunately, it doesn't work on Linux.
Thanks, Gerry
From: Tomaž Turk <tomaz.turk@ef.uni-lj.si> Sent: Sunday, November 28, 2021 11:39 AM To: Any question about pharo is welcome <pharo-users@lists.pharo.org> Subject: [Pharo-users] Re: uFFI provide buffer to C
Hi,
try with this:
FFITutorial>>getHostNameInto: hostName ofLenght: length ^self ffiCall: #( int gethostname(char *hostName, int length) ) library: 'Ws2_32.dll'. "... on Windows"
From Playground, you can then do:
| name len | len := 50. name:= ByteArray new: len. FFITutorial new getHostNameInto: name ofLenght: len. name inspect.
I hope this helps.
Best wishes, Tomaz