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• Writing a VM - well formed bytecode?

  - by David Titarenco

  Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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• How to initialize a static const map in c++?

  - by Meloun

  Hi, I need just dictionary or asociative array string = int. There is type map C++ for this case. But I need make one map in my class make for all instances(- static) and this map cannot be changed(- const); I have found this way with boost library std::map<int, char> example = boost::assign::map_list_of(1, 'a') (2, 'b') (3, 'c'); Is there other solution without this lib? I have tried something like this, but there are always some issues with map initialization. class myClass{ private: static map<int,int> create_map() { map<int,int> m; m[1] = 2; m[3] = 4; m[5] = 6; return m; } static map<int,int> myMap = create_map(); } thanks

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• Get the lua command when a c function is called

  - by gamernb

  Supposed I register many different function names in Lua to the same function in C. Now, everytime my C function is called, is there a way to determine which function name was invoked? for example: int runCommand(lua_State *lua) { const char *name = // getFunctionName(lua) ? how would I do this part for(int i = 0; i < functions.size; i++) if(functions[i].name == name) functions[i].Call() } int main() { ... lua_register(lua, "delay", runCommand); lua_register(lua, "execute", runCommand); lua_register(lua, "loadPlugin", runCommand); lua_register(lua, "loadModule", runCommand); lua_register(lua, "delay", runCommand); } So, how do I get the name of what ever function called it?

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• How can I ensure that a Java object (containing cryptographic material) is zeroized?

  - by Jeremy Powell

  My concern is that cryptographic keys and secrets that are managed by the garbage collector may be copied and moved around in memory without zeroization. As a possible solution, is it enough to: public class Key { private char[] key; // ... protected void finalize() throws Throwable { try { for(int k = 0; k < key.length; k++) { key[k] = '\0'; } } catch (Exception e) { //... } finally { super.finalize(); } } // ... }

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• gcc, UTF-8 and limits.h

  - by bobby

  My OS is Debian, my default locale is UTF-8 and my compiler is gcc. By default CHAR_BIT in limits.h is 8 which is ok for ASCII because in ASCII 1 char = 8 bits. But since I am using UTF-8, chars can be up to 32 bits which contradicts the CHAR_BIT default value of 8. If I modify CHAR_BIT to 32 in limits.h to better suit UTF-8, what do I have to do in order for this new value to come into effect ? I guess I have to recompile gcc ? Do I have to recompile the linux kernel ? What about the default installed Debian packages, will they work ?

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• Is Boost.Tuple compatible with C++0x variadic templates ?

  - by Thomas Petit

  Hi, I was playing around with variadic templates (gcc 4.5) and hit this problem : template <typename... Args> boost::tuple<Args...> my_make_tuple(Args... args) { return boost::tuple<Args...>(args...); } int main (void) { boost::tuple<int, char> t = my_make_tuple(8, 'c'); } GCC error message : sorry, unimplemented: cannot expand 'Arg ...' into a fixed-length argument list In function 'int my_make_tuple(Arg ...)' If I replace every occurrence of boost::tuple by std::tuple, it compiles fine. Is there a problem in boost tuple implementation ? Or is this a gcc bug ? I must stick with Boost.Tuple for now. Do you know any workaround ? Thanks.

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• How to keep historic details of modification in a database (Audit trail)?

  - by mada

  I'm a J2EE developer & we are using hibernate mapping with a PostgreSQL database. We have to keep track of any changes occurs in the database, in others words all previous & current values of any field should be saved. Each field can be any type (bytea, int, char...) With a simple table it is easy but we a graph of objects things are more difficult. So we have, speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that?

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• Retrieving datatypes from underlying database

  - by H4mm3rHead

  Hi, Im making an application that displays information about an underlying database. The database can be anything, but is typically either Oracle, MSSQL or MySQL. I am trying to extract the datatype but cannot seem to get this right. I have a DbConnection because i dont know whether I need a OleDbConnection or an OdbcConnection. On this connection I make a GetSchema("Columns", "mytablename") query and gets the result back. It seems though that there are some inconsistencies with my datatypes or the query returns different datatypes for the different databases. For instance, in my MSSQL database I query and get an integer back (which seems to be the OleDbType) which I map to a datatype. My varchars is now of type char - no length - and this confuses me a bit. I guess my main question is something like: Is there any way of making a uniform way of extracting datatypes across providers and having an "accurate" representation of the datatype?

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• difference fixed width strings and zero-terminated strings

  - by robUK

  Hello, gcc 4.4.4 c89 I got into a recent discussion about "fixed width strings" and "zero terminated strings". When I think about this. They seem to be the same thing. A string with a terminating null. i.e. char *name = "Joe bloggs"; Is a fixed width string that cannot be changed. And also has a terminating null. Also in the discussion I was told that strncpy should never been used on 'zero terminated strings'. Many thanks for any susgestions,

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• Unit Testing Private Method in Resource Managing Class (C++)

  - by BillyONeal

  I previously asked this question under another name but deleted it because I didn't explain it very well. Let's say I have a class which manages a file. Let's say that this class treats the file as having a specific file format, and contains methods to perform operations on this file: class Foo { std::wstring fileName_; public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it //Long method to figure out what checksum it is. //Return the checksum. } }; Let's say I'd like to be able to unit test the part of this class that calculates the checksum. Unit testing the parts of the class that load in the file and such is impractical, because to test every part of the getChecksum() method I might need to construct 40 or 50 files! Now lets say I'd like to reuse the checksum method elsewhere in the class. I extract the method so that it now looks like this: class Foo { std::wstring fileName_; static int calculateChecksum(const std::vector<unsigned char> &fileBytes) { //Long method to figure out what checksum it is. } public: Foo(const std::wstring& fileName) : fileName_(fileName) { //Construct a Foo here. }; int getChecksum() { //Open the file and read some part of it return calculateChecksum( something ); } void modifyThisFileSomehow() { //Perform modification int newChecksum = calculateChecksum( something ); //Apply the newChecksum to the file } }; Now I'd like to unit test the calculateChecksum() method because it's easy to test and complicated, and I don't care about unit testing getChecksum() because it's simple and very difficult to test. But I can't test calculateChecksum() directly because it is private. Does anyone know of a solution to this problem?

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• Initialize a static member ( an array) in C++

  - by Jimmy zhang

  I intended to create a class which only have static members and static functions. One of the member variable is an array. Would it be possible to initialize it without using constructors? I am having lots of linking errors right now... Class A{ public: static char a[128]; static void do_something(); } How would you initialize a[128]? Why can't I initialize a[128] by directly specifying its value like in C? a[128={1,2,3,...};

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• Why does this give a segmentation fault?

  - by nightcracker

  I'm stunned, why does this code give me a segmentation fault? #include <stdio.h> #define LIMIT 1500000 typedef struct { int p; int a; int b; } triplet; int main(int argc, char **argv) { int i; triplet triplets[LIMIT]; for (i = 0; i < 5; i++) { triplets[i].p = 9; // remove this line and everything works fine } printf("%d\n", triplets[15].p); return 0; } EDIT: After changing LIMIT to 150 I no longer get a segmentation fault, it prints random numbers instead.

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• Counting characters in an Access database column using SQL

  - by jzr

  I have the following table col1 col2 col3 col4 ==== ==== ==== ===== 1233 4566 ABCD CDEF 1233 4566 ACD1 CDEF 1233 4566 D1AF CDEF I need to count the characters in col3, so from the data in the previous table it would be: char count ==== ===== A 3 B 1 C 2 D 3 F 1 1 2 Is this possible to achieve by using SQL only? At the moment I am thinking of passing a parameter in to SQL query and count the characters one by one and then sum, however I did not start the VBA part yet, and frankly wouldn't want to do that. This is my query at the moment: PARAMETERS X Long; SELECT First(Mid(TABLE.col3,X,1)) AS [col3 Field], Count(Mid(TABLE.col3,X,1)) AS Dcount FROM TEST GROUP BY Mid(TABLE.col3,X,1) HAVING (((Count(Mid([TABLE].[col3],[X],1)))>=1)); Ideas and help are much appreciated, as I don't usually work with Access and SQL.

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• QT4 Designer - Implement Widget

  - by MOnsDaR

  I'm currently trying to get into QT4 and figure out a workflow for myself. While trying to create a widget which allows the user to connect to a hostname:port some questions appeared. The widget itself contains a LineEdit for entering the hostname, a SpinBox for entering the port and a PushButton which should emit a connect(QString hostname, unsigned int port) signal. In QTDesigner I created the necessary Form. It is saved as a .ui-File. Now the big question is how could I implement the widget? Is there a place in QTDesigner where I could add my signal to the Widget? Where could I add custom Properties? I've learned in another tutorial, which showed how to create a Widget in C++, how signals, slots, Q_PROPERTIES etc are defined and added to the widget. But there is no sourcecode in QTDesigner. Another option would be to generate sourcecode using uic. But the header says, that another generate would overwrite any changes to the sourcefiles. So how can I create a QT-widget completely with my own signals, slots and properties by using the QTDesigner for creating the UI and not having to recode everything whenever the UI is changing. Is there some kind of Roundtrip-Engineering? If thats not possible: Whats the sense of creating a Widget with QTDesigner then?

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• const read only local copies

  - by robUK

  Hello gcc 4.4.4 c89 I am just wondering is it worth passing a const into a function. i.e. void do_something(const char *dest, const int size) The size is a read-only so I don't want to change it. However, some developers never have this as const has it is a local copy that is being used. The pointer is const as you can change the value in the calling routine. I always have a const on read-only local copies, as it confirms to anyone reading my code that it is a read-only variable. And also, when coding I don't make the mistake of changing it without realizing. Many thanks for any suggestions,

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• fesetround with MSVC x64

  - by mr grumpy

  I'm porting some code to Windows (sigh) and need to use fesetround. MSVC doesn't support C99, so for x86 I copied an implementation from MinGW and hacked it about: //__asm__ volatile ("fnstcw %0;": "=m" (_cw)); __asm { fnstcw _cw } _cw &= ~(FE_TONEAREST | FE_DOWNWARD | FE_UPWARD | FE_TOWARDZERO); _cw |= mode; //__asm__ volatile ("fldcw %0;" : : "m" (_cw)); __asm { fldcw _cw } if (has_sse) { unsigned int _mxcsr; //__asm__ volatile ("stmxcsr %0" : "=m" (_mxcsr)); __asm { stmxcsr _mxcsr } _mxcsr &= ~ 0x6000; _mxcsr |= (mode << __MXCSR_ROUND_FLAG_SHIFT); //__asm__ volatile ("ldmxcsr %0" : : "m" (_mxcsr)); __asm { ldmxcsr _mxcsr } } The commented lines are the originals for gcc; uncommented for msvc. This appears to work. However the x64 cl.exe doesn't support inline asm, so I'm stuck. Is there some code out there I can "borrow" for this? (I've spent hours with Google). Or will I have to go on a 2 week detour to learn some assembly and figure out how to get/use MASM? Any advice is appreciated. Thank you.

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• Typical text encoding and EOL behavior on mobile devices

  - by Dan W

  Typical things to worry about when dealing with text are the BOM/signature, encoding, and the end of line (EOL) char/chars. I know that Windows often favours \r\n (CR+LF) and Mac/Linux favours \n (LF), but how about popular mobile devices such as the iPhone and Android? Do typical apps on those platforms favour one or the other (or maybe even \r for iOS)? I'll supply both types to the user just in case, but I'd like to choose one as default. Also, which text encodings are mobiles most likely to use - UTF-8, iso-8859-1, Windows 1252 (or other default codepage) or maybe even UTF-16? And if they use UTF-8/16, are they likely to need (or require not having) a BOM/signature? What is the typical behavior here? Once again, I'll supply a range of encodings to the user just in case, but I'd like to prioritize or use certain encodings as default if it's appropriate.

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• charset problem?

  - by Ben Fransen

  Hi all, I have a bugging problem. For a website I made there are search engine friendly URL's generated. The only problem is there are ß-chars in the url too. Chars like ö, ï, ä, ü etc. are placed correct. But with the ß-char there is a diamond-icon with a questionmark in it. I thought it had to do with the charset which is used but i've tried both UTF-8 and iso-8859-1. Both without luck. I need to have the correct character in the url for the readability of deeplinks. Hope to hear from you!

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• Consolidate loan, purchase & sale tables into one transaction table.

  - by Frank Computer

  INFORMIX-SE with ISQL 7.3: I have separate tables for Loan, Purchase & Sales transactions. Each tables rows are joined to their respective customer rows by: customer.id [serial] = loan.foreign_id [integer]; = purchase.foreign_id [integer]; = sale.foreign_id [integer]; I would like to consolidate the three tables into one table called "transaction", where a column: transaction.trx_type char(1) {L=Loan, P=Purchase, S=Sale} identifies the transaction type. Each transaction will be assigned a unique transaction number [serial]. Is this a good idea or is it better to keep them in separate tables? Storage space is not a concern, I think it would be easier programming & user-wise to have all types of transactions under one table, whenever possible. This implies denormalization.

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• Using WINAPI ReadConsole

  - by Jim Fell

  I am trying to use the WINAPI ReadConsole() to wait for any keypress at the end of my Win32 console application. CONSOLE_READCONSOLE_CONTROL tControl; char pStr[65536]; DWORD dwBufLen = 1; DWORD dwCtl; tControl_c.nLength = sizeof( CONSOLE_READCONSOLE_CONTROL ); tControl_c.nInitialChars = 0; tControl_c.dwControlKeyState = 0; tControl_c.dwCtrlWakeupMask = NULL; pBuf[0] = 0x00; do { ReadConsole( hConsole_c, pStr, (*pBufLen) * sizeof(TCHAR), pBufLen, &tControl ); } while ( pStr[0] == 0x00 ); The code executes without throwing an exception. However, when the ReadConsole() function executes the error code ERROR_INVALID_HANDLE (0x06) is flagged. I have verified hConsole_c to be a valid handle. Does anyone have any insight as to what I am doing wrongly? I am using Visual C++ 2008 Express Edition. Thanks.

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• Unicode and PHP - am I doing something wrong?

  - by alex

  I'm using Kohana 3, which has full support for Unicode. I have this as the first child of my <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> The Unicode character I am inserting into is é as in Café. However, I am getting the triangle with a ? (as in could not decode character). As far as I can tell in my own code, I am not doing any string manipulation on the text. In fact, I have placed the accent straight into a view's PHP file and it is still not working. I copied the character from this page: http://www.fileformat.info/info/unicode/char/00e9/index.htm I've only just started examining PHP's Unicode limitations, so I could be doing something horribly wrong. So, how do I display this character? Do I need to resort to the HTML entity?

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• Perl, treat string as binary byte array

  - by Mike

  In Perl, is it appropriate to use a string as a byte array containing 8-bit data? All the documentation I can find on this subject focuses on 7-bit strings. For instance, if I read some data from a binary file into $data my $data; open FILE, "<", $filepath; binmode FILE; read FILE $data 1024; and I want to get the first byte out, is substr($data,1,1) appropriate? (again, assuming it is 8-bit data) I come from a mostly C background, and I am used to passing a char pointer to a read() function. My problem might be that I don't understand what the underlying representation of a string is in Perl.

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• Python/C "defs" file - what is it?

  - by detly

  In the nautilus-python bindings, there is a file "nautilus.defs". It contains stanzas like (define-interface MenuProvider (in-module "Nautilus") (c-name "NautilusMenuProvider") (gtype-id "NAUTILUS_TYPE_MENU_PROVIDER") ) or (define-method get_mime_type (of-object "NautilusFileInfo") (c-name "nautilus_file_info_get_mime_type") (return-type "char*") ) Now I can see what most of these do (eg. that last one means that I can call the method "get_mime_type" on a "FileInfo" object). But I'd like to know: what is this file, exactly (ie. what do I search the web for to find out more info)? Is it a common thing to find in Python/C bindings? What is the format, and where is it documented? What program actually processes it? (So far, I've managed to glean that it gets transformed into a C source file, and it looks a bit like lisp to me.)

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• dangling pointer, reason for value change after free()?

  - by Aman Jain

  In the following code segment, after free(x), why does y becomes 0? As per my understanding, the memory in the heap that was being pointed to by x, and is still being pointed by y, hasn't been allocated to someone else, so how can it change to 0? And moreover, I don't think it is free(x) that changed it to 0. Any comments? #include <stdio.h> int main ( int argc, char *argv[] ) { int *y = NULL; int *x = NULL; x = malloc(4); *x = 5; y = x; printf("[%d]\n", *y); //prints 5 free(x); printf("[%d]\n", *y); //why doesn't print 5?, prints 0 instead return 0; }

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• mysql query help, take total sum from a table, and based on discount value on another table calcula

  - by vegatron

  hi I have a table called invoices: CREATE TABLE IF NOT EXISTS `si_invoices` ( `id` int(10) NOT NULL AUTO_INCREMENT, `biller_id` int(10) NOT NULL DEFAULT '0', `customer_id` int(10) NOT NULL DEFAULT '0', `type_id` int(10) NOT NULL DEFAULT '0', `inv_tax_id` int(10) NOT NULL, `date` date NOT NULL DEFAULT '0000-00-00', `unreg_customer` tinyint(1) NOT NULL DEFAULT '0', `discount` decimal(10,2) NOT NULL DEFAULT '0.00', `discount_type` tinyint(1) NOT NULL DEFAULT '0', PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=20 ; each invoice has items that are stored in invoice_items table : CREATE TABLE IF NOT EXISTS `si_invoice_items` ( `id` int(10) NOT NULL AUTO_INCREMENT, `invoice_id` int(10) NOT NULL DEFAULT '0', `quantity` int(10) unsigned NOT NULL DEFAULT '0', `product_id` int(10) DEFAULT '0', `warehouse_id` int(10) NOT NULL, `unit_price` decimal(25,2) DEFAULT '0.00', `total` decimal(25,2) DEFAULT '0.00', `description` text, PRIMARY KEY (`id`), KEY `invoice_id` (`invoice_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=56 ; and tax table CREATE TABLE IF NOT EXISTS `si_tax` ( `tax_id` int(11) NOT NULL AUTO_INCREMENT, `tax_description` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL, `tax_percentage` decimal(25,6) DEFAULT '0.000000', `type` varchar(1) COLLATE utf8_unicode_ci DEFAULT NULL, `tax_enabled` varchar(1) COLLATE utf8_unicode_ci NOT NULL DEFAULT '1', PRIMARY KEY (`tax_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=5 ; here is what I want to do step 1: get the sum_total of the invoice Items for a speciefic invoice step 2: calculate the discount, in the invoice table I have a discount_type field : if its equal to 0 , then there will be no discount if its equal to 1 , the discount value will be stored in the discount field if its equal to 2 , the discount is a percentage of sum_total step 3: calculate the taxes based on inv_tax_id based on the tax id , I will look in the tax table , get the tax_percentage and multiply it by the (sum_total - discount) in short here is the equation $gross_total = $sum_total - $disount + taxes

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