Need help mapping a struct for platform functions
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Hi,
I need to pass a struct to a library function that looks like this: typedef struct { unsigned short preview; const char* filename;} myparameter;As far as I understand things now, I need to subclass OSStructure. Here's what I have so far: OSStructure subclass: #MyParameter instanceVariableNames: '' classVariableNames: '' poolDictionaries: ''! !MyParameter class publicMethods ! initializeAfterLoad "self initializeAfterLoad" self fixedSize: 6; members: #(#preview #filename).! ! !MyParameter publicMethods ! initialize self preview: false. self filename: './temp.pdf'. ! filename ^(self uint32At: 2) asString! filename: einString ^self uint32At: 4 put: einString asPSZ! preview ^(self uint16At: 0) = 1! preview: aBool ^self uint16At: 0 put: (aBool ifTrue: [1] ifFalse: [0])! ! MyParameter initializeAfterLoad! So far, getting and setting the boolean parameter (preview) seems to work, but I struggle with the String parameter. So here are my questions: Are my assumptions correct about the sizes/types: unsigned short = unit16, char * = uint32? Is the setter for the string (#filename:) correct? I guess the answer is NO, but I don't know what else to do. When I have to pass this struct to a platform function, do I define the parameter as a #pointer ? (My guess would be YES) Do I free OSStructure instances after each call? Thanks for answering Joachim -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/2aWUMd-YvKwJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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Hi Joachim...did you intend '4' to be '2' in the filename: setter ??
-- Seth On Tuesday, October 2, 2012 10:05:00 AM UTC-4, [hidden email] wrote: Hi, You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/G9diNDghJlAJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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In reply to this post by jtuchel
Joachim - You need to account for data alignment in the struct. There will be 2 bytes of padding between preview and filename (because 32-bit pointers are 4-byte aligned). So the actual size of the struct is 8, not 6, and filename is at offset 4. On Tuesday, October 2, 2012 10:05:00 AM UTC-4, [hidden email] wrote: Hi,-- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/vtlwSJ0LHegJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
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In reply to this post by Seth Berman
Hi Seth,
in fact, I wanted it to be 2, but if I understand John's answer correctly, I need to always allow 4 bytes for a pointer, even if it is smaller. So I guess they all should be multiples of 4... Thanks for taking your time to answer. Joachim Am Dienstag, 2. Oktober 2012 18:27:36 UTC+2 schrieb Seth Berman: Hi Joachim...did you intend '4' to be '2' in the filename: setter ??-- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/LEkVPUZHSmQJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
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In reply to this post by John O'Keefe-3
Hi John,
thanks for this info. So I changed the struct sizes, and I also found some code that helped me get getter and setter to work (as long as I do not make a call). For setting char * in the struct I use: self uint32At: 4 put: aString asPSZ copyToOSMemory. and for reading it back from the structure, I use: (OSStringZ address: (self uint32At: 4)) asString Is this the right way to do it? I guess I have to free these instances of OSStringZ? What if I have really big text parameters (starting at 20K, including a full xml file)? Do I reuse these or free them or simplz not care? Joachim Am Dienstag, 2. Oktober 2012 18:58:41 UTC+2 schrieb John O'Keefe: -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/v8Q1stiKCaMJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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In reply to this post by John O'Keefe-3
But the first member of the struct is defined as unsigned short, not a pointer, so your initial size and offset were good. Normand On Tuesday, October 2, 2012 12:58:41 PM UTC-4, John O'Keefe wrote: -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/y8ysLBoeRq4J. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
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Normand,
at least moving the second entry to offset 4 didn't hurt. Thanks to the tips on tnis thread, I could make my code run and I am now redy to send long xml strings to the dll and receive lots of error messages from the library :-) I am still a bit unsure about the freeing question. Should I reuse an instance of OSStringZ with 40K or realllocate a new one for eac call? This function will have to be called several hundreds of times per day on a web server... Joachim Am Mittwoch, 3. Oktober 2012 15:02:40 UTC+2 schrieb Normand Mongeau: -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/qsXo8N2hrRkJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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New instance ....
Marten -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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In reply to this post by jtuchel
Hmmmmmm ???
Marten Am Freitag, 5. Oktober 2012 07:03:54 UTC+2 schrieb [hidden email]: Normand,-- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/0Ens3VNI__8J. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
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Hi Marten,
Did I say something stupid (again)? My current (seemingly running) implementation leaves a gap of two bytes between the Boolean and the String parameters (offsets 0 and 4). So far, doing a few dozen calls did not crash or return any strange results. Do you mean that having these two bytes unused in the middle of the struct is wrong/dangerous/unpredictable/unethical or a bad idea for any other reason? Joachim Am Freitag, 5. Oktober 2012 09:56:33 UTC+2 schrieb Marten Feldtmann: Hmmmmmm ???-- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/5hvPrJJcHH4J. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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It should be (we are working on 32 bit systems):
* on the Smalltalk side I would expect byte offset 0 and 2 * a short is normally 2 bytes aligned * a pointer is normally 4 bytes aligned and an offset of 4 is strange (i think its a typing error). Marten As a reference what might happens here: http://en.wikipedia.org/wiki/Data_structure_alignment#Data_structure_padding -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
Re: Need help mapping a struct for platform functions
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Hmm, that was bulshit.
The structure itself is already located with an aligment suitable for the largest member of the structure - here a pointer with a 4 byte alignment. start of the structure (4 byte aligned) +0 - short +1 - short +2 - local structure alignment padding due to following pointer +3 - local structure alignment padding due to following pointer +4 - pointer +5 - pointer +6 - pointer +7 - pointer Therefore the size of the structure is 8 bytes and the offsets to the data elements are "0" and "4". Am Freitag, 5. Oktober 2012 12:13:01 UTC+2 schrieb Marten Feldtmann: -- You received this message because you are subscribed to the Google Groups "VA Smalltalk" group. To view this discussion on the web visit https://groups.google.com/d/msg/va-smalltalk/-/tkhYmcOtO7AJ. To post to this group, send email to [hidden email]. To unsubscribe from this group, send email to [hidden email]. For more options, visit this group at http://groups.google.com/group/va-smalltalk?hl=en. |
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