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ndudman
Joined: 25 Dec 2008
Posts: 79
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Posted: 10 January 2009, 10:19 AM Post subject: Passing const char* c->zbasic |
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Hi Iḿ trying to write the following sub... which is called from some c code and intended to pass a const char* into zbasic. Am I heading in the write direction ? Not sure if Ive got the if check for str termination correct or if the subroutine parameter declaration is ok. Im not able to test it yet to determine if it works, although Im sure I am missing something
| Code: | '~ To be called from the Menu_imp.c which needs to pass
'~ a const char* to this zbasic subroutine
'~ The generated c function should have prototype (void)(const char*)
public sub DisplayStr_C(byval strPtr as UnsignedInteger)
Dim d() as Byte Based strPtr
Dim str as String = ""
Dim i as byte = 0
do
if (d(i) = 0) then
exit do
end if
str = str & d(i)
i = i + 1
loop
call DisplayStr(str)
end sub |
Thanks
Neil |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 10 January 2009, 16:32 PM Post subject: |
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There were a couple of minor problems in the proposed subroutine which I've fixed in the rendition below. The first is that the array d() is 1-based in ZBasic so the variable i must be initialized to 1. The second problem is that you must use the Chr() function when you append the characters to the string. | Code: | Public Sub DisplayStr_C(ByVal strAddr as UnsignedInteger)
Dim d() as Byte Based strAddr
Dim str as String = ""
Dim i as byte = 1
Do
If (d(i) = 0) Then
Exit Do
End If
str = str & Chr(d(i))
i = i + 1
Loop
Call DisplayStr(str)
End Sub |
As for the const char * formal parameter needed by your C calling routine, it wouldn't make sense for ZBasic to generate code with a const char * parameter corresponding to a ZBasic integral value. If we did, then code that needed to modify the memory at that address wouldn't work.
The solution is to introduce an intermediary function in your C code that takes a const char * parameter and casts it to an integral value to match the ZBasic subroutine parameter. The example code below may work for that purpose. Depending on how it is used in the C code you may be able to replace it with a #define. | Code: | void
intermediary(const char *str)
{
zf_DisplayStr_C((uint16_t)(void *)str);
} |
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ndudman
Joined: 25 Dec 2008
Posts: 79
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Posted: 10 January 2009, 17:53 PM Post subject: |
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Thanks again
Pleased that i wasnt too far off... but really helped to iron out those things for me.
Regards
Neil |
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