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• [C++] instantiating bitset using hex character.

  - by bndz

  Hey, I'm trying to figure out how to instantiate a 4 bit bitset based on a hex character. For instance, If I have a character with value 'F', I want to create a bitset of size 4 initialized to 1111 or if it is A, i want to initialize it to 1010. I could use a bunch of if statements like so: fn(char c) { bitset<4 temp; if(c == 'F') temp.set(); //... if(c == '9') { temp.set(1); temp.set(3); } //... } This isn't efficient, is there a way of easily converting the string to a decimal integer and constructing the bitset using the last 4 bits of the int? Thanks for any help.

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• IE error with jquery counter plugin

  - by Mankey

  I've implemented a jquery counter script (count up from say 50 to 100 with different increments) that I found from this question: jQuery counter to count up to a target number The scripts works great except for in Internet Explorer 8 (and possibly other IE versions?). Here's an error message from IE with the URL to the creator of the script's demo. Message: 'undefined' is null or not an object Line: 32 Char: 17 Code: 0 URI: http://www.ulmanen.fi/stuff/counter.php I'm just wondering if anyone know how this can be fixed. I'm guessing it has to do with el.html() not finding any data but I can't really figure this out. Thanks for any help ^^ I would reply to that post if I could but I can't seem to find any way of doing so (I'm new to stackoverflow, I think I lack privileges).

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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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• 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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• va_arg with pointers

  - by Yktula

  I want to initialize a linked list with pointer arguments like so: /* * Initialize a linked list using variadic arguments * Returns the number of structures initialized */ int init_structures(struct structure *first, ...) { struct structure *s; unsigned int count = 0; va_list va; va_start(va, first); for (s = first; s != NULL; s = va_arg(va, (struct structure *))) { if ((s = malloc(sizeof(struct structure))) == NULL) { perror("malloc"); exit(EXIT_FAILURE); } count++; } va_end(va); return count; } The problem is that clang errors type name requires a specifier or qualifier at va_arg(va, (struct structure *)), and says that the type specifier defaults to int. It also notes instantiated form at (struct structure *) and struct structure *. This, what seems to be getting assigned to s is int (struct structure *). It compiles fine when parentheses are removed from (struct structure *), but the structures that are supposed to be initialized are inaccessible. Why is int assumed when parentheses are around the type argument passed to va_arg? How can I fix this?

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• c++ library for endian-aware reading of raw file stream metadata?

  - by Kache4

  I've got raw data streams from image files, like: vector<char> rawData(fileSize); ifstream inFile("image.jpg"); inFile.read(&rawData[0]); I want to parse the headers of different image formats for height and width. Is there a portable library that can can read ints, longs, shorts, etc. from the buffer/stream, converting for endianess as specified? I'd like to be able to do something like: short x = rawData.readLeShort(offset); or long y = rawData.readBeLong(offset) An even better option would be a lightweight & portable image metadata library (without the extra weight of an image manipulation library) that can work on raw image data. I've found that Exif libraries out there don't support png and gif.

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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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• 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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• 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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• Put logic behind generated LinqToSql fields

  - by boris callens

  In a database I use throughout several projects, there is a field that should actually be a boolean but is for reasons nobody can explain to me a field duplicated over two tables where one time it is a char ('Y'/'N') and one time an int (1/0). When I generate a datacontext with LinqToSql the fields off course gets these datatypes. It would be nice if I don't have to drag this stupid choice of datatype throughout the rest of my application. Is there a way to give the generated classes a little bit of logic that just return me return this.equals('Y'); and return this==1; Preferably without having to make an EXTRA field in my partial class. It would be a solution to give the generated field a totally different name that can only be accessed through the partial class and then generate the extra field with the original name with my custom logic in the partial class. I don't know how to alter the accesibility level in my generated class though.. Any suggestions?

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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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• 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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• 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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• 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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• 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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• 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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• Passing a 2D array to a function in C

  - by Tyler Treat

  I have, essentially, a matrix of data (lets say ints) that I would like to store in a 2D array in which the dimensions are not known until runtime (say x columns and y rows). I want to populate the array in a function, so I assume I need to do something like this: int main(int argc, char **argv) { int y = atoi(argv[1]); int x = atoi(argv[2]); int **matrix = malloc(x * sizeof(int*)); populateMatrix(matrix, y, x); return 0; } void populateMatrix(**matrix, int y, int x) { int i, j; for (i = 0; i < y; i++) { for (j = 0; j < x; j++) { matrix[i][j] = i * j; // populated with trivial data to keep it simple } } } Obviously this doesn't work, but I'm not sure how to do what I'm describing exactly.

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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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• 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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• 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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• Using NULLs in matchup table

  - by TomWilsonFL

  I am working on the accounting portion of a reservation system (think limo company). In the system there are multiple objects that can either be paid or submit a payment. I am tracking all of these "transactions" in three tables called: tx, tx_cc, and tx_ch. tx generates a new tx_id (for transaction ID) and keeps the information about amount, validity, etc. Tx_cc and tx_ch keep the information about the credit card or check used, respectively, which link to other tables (credit_card and bank_account among others). This seems fairly normalized to me, no? Now here is my problem: The payment transaction can take place for a myriad of reasons. Either a reservation is being paid for, a travel agent that booked a reservation is being paid, a driver is being paid, etc. This results in multiple tables, one for each of the entities: agent_tx, driver_tx, reservation_tx, etc. They look like this: CREATE TABLE IF NOT EXISTS `driver_tx` ( `tx_id` int(10) unsigned zerofill NOT NULL, `driver_id` int(11) NOT NULL, `reservation_id` int(11) default NULL, `reservation_item_id` int(11) default NULL, PRIMARY KEY (`tx_id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; Now this transaction is for a driver, but could be applied to an individual item on the reservation or the entire reservation overall. Therefore I demand either reservation_id OR reservation_item_id to be null. In the future there may be other things which a driver is paid for, which I would also add to this table, defaulting to null. What is the rule on this? Opinion? Obviously I could break this out into MANY three column tables, but the amount of OUTER JOINing needed seems outrageous. Your input is appreciated. Peace, Tom

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• setting a timeout for an InputStreamreader variable

  - by Noona

  I have a server running that accepts connections made through client sockets, I need to read the input from this client socket, now suppose the client opened a connection to my server without sending anything through the server's socket outputstream, in this case, while my server tried to read the input through the client socket's inputstream, an exception will be thrown, but before the exception is thrown i would like a timeout say of 5 sec, how can I do this? currently here's how my code looks like on the server side: try { InputStreamReader clientInputStream = new InputStreamReader(clientSocket.getInputStream()); int c; StringBuffer requestBuffer = new StringBuffer(); while ((c = clientInputStream.read()) != -1) { requestBuffer.append((char) c); if (requestBuffer.toString().endsWith(("\r\n\r\n"))) break; } request = new Request(requestBuffer.toString(), clientSocket); } catch (Exception e) // catch any possible exception in order to keep the thread running { try { if (clientSocket != null) clientSocket.close(); } catch (IOException ex) { ex.printStackTrace(); } System.err.println(e); //e.printStackTrace(); }

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• lua string printing

  - by anon

  In C, I have format strings, something like: char *msg = "wlll you marry me" fprintf(stderr, "%s, %s?", name, msg); Now, can I do something similar in lua with format strings? I.e. I want something functionally equivalent to: name .. ", " .. msg .. "?" but not so ugly, in lua. Okay, so I can do string.format("%s, %s?", name, msg), but can I go even a step further, something like perl style, where I can go: "%name, %msg?" Thanks!

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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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