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• `.' cannot appear in a constant-expression

  - by Amir Rachum

  Hi all, I'm getting the following error: `.' cannot appear in a constant-expression for this function (line 4): bool Covers(const Region<C,V,D>& other) const { const Region& me = *this; for (unsigned d = 0; d < D; d++) { if (me[d].min > other[d].min || me[d].max < other[d].max) { return false; } } can anyone explain the problem please?

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• Why MySQL multiple-column index is overpopulated?

  - by actual

  Consider following MySQL table: CREATE TABLE `log` ( `what` enum('add', 'edit', 'remove') CHARACTER SET ascii COLLATE ascii_bin NOT NULL, `with` int(10) unsigned NOT NULL, KEY `with_what` (`with`,`what`) ) ENGINE=InnoDB; INSERT INTO `log` (`what`, `with`) VALUES ('add', 1), ('edit', 1), ('add', 2), ('remove', 2); As I understand, with_what index must have 2 unique entries on its first with level and 3 unique entries in what "subindex". But MySQL reports 4 unique entries for each level. In other words, number of unique elements for each level is always equal to number of rows in log table. Is that a bug, a feature or my misunderstanding?

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• How i store the images pixels in matrix form?

  - by Rajendra Bhole

  Hi, I developing an application in which the pixelize image i want to be store in matrix format. The code is as follows. struct pixel { //unsigned char r, g, b,a; Byte r, g, b; int count; }; (NSInteger) processImage1: (UIImage*) image { // Allocate a buffer big enough to hold all the pixels struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel)); if (pixels != nil) { // Create a new bitmap CGContextRef context = CGBitmapContextCreate( (void*) pixels, image.size.width, image.size.height, 8, image.size.width * 4, CGImageGetColorSpace(image.CGImage), kCGImageAlphaPremultipliedLast ); NSLog(@"1=%d, 2=%d, 3=%d", CGImageGetBitsPerComponent(image), CGImageGetBitsPerPixel(image),CGImageGetBytesPerRow(image)); if (context != NULL) { // Draw the image in the bitmap CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage); NSUInteger numberOfPixels = image.size.width * image.size.height; I confusing about how to initialize the 2-D matrix in which the matrix store data of pixels.

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• Where does output of print in kernel go?

  - by apoorv020

  I am debugging a driver for linux (specifically ubuntu server 9.04), and there are several printf statements in the code. Where can I view the output of these statements? EDIT1: What i'm trying to do is write to kernel using the proc file-system. The print code is static int proc_fractel_config_write(struct file *file, const char *argbuf, unsigned long count, void *data) { printk(KERN_DEBUG "writing fractel config\n"); ... In kern.log when I see the following message when i try to overwrite the file /proc/net/madwifi/ath1/fractel_config (with varying time of course). [ 8671.924873] proc write [ 8671.924919] Any explainations?

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• bitfield mask calculation macro

  - by Aidan Cully

  We have a set of C macros, here, for using the preprocessor to do bitfield operations, and we run into warnings when attempting to use these macros in visual studio. The problem can be demonstrated very easily: #define BITFIELD_WIDTHMASK(Width) \ ((Width) >= 32 ? ~0x0ul : (1ul << (Width)) - 1) unsigned long foo(void) { return BITFIELD_WIDTHMASK(32); } Compiling this with MSVC yields the warning: test.c(12) : warning C4293: '<<' : shift count negative or too big, undefined behavior This isn't a behavior problem - the << operator won't be used in this case, and that should be detected at compile time. But does anyone have any suggestions about how to rewrite the macro to avoid the warning? Or, failing that, how to redesign the macro interface for this? Thanks in advance

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• How to make this jpeg compression faster

  - by Richard Knop

  I am using OpenCV to compress binary images from a camera: vector<int> p; p.push_back(CV_IMWRITE_JPEG_QUALITY); p.push_back(75); // JPG quality vector<unsigned char> jpegBuf; cv::imencode(".jpg", fIplImageHeader, jpegBuf, p); The code above compresses a binary RGB image stored in fIplImageHeader to a JPEG image. For a 640*480 image it takes about 0.25 seconds to execute the five lines above. Is there any way I could make it faster? I really need to repeat the compression more than 4 times a second.

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• Why am I not getting correct result when I calculate exponent with ^ in C++?

  - by xbonez

  I am using Bode's formuala to calculate distance of nth planet from sun dist = (4 + 3*(2^(n-2)))/10 If I calculate the distance this way, I get the right values: dist[2] = ((4 + 3*1)/10.0) ; dist[3] = ((4 + 3*2)/10.0) ; dist[4] = ((4 + 3*4)/10.0) ; But doing it this way, gives me incorrect values: vector <double> dist(5); for (unsigned int i = 2; i < 5; i++) { dist[i] = ((4 + 3*(2^(3-2)))/10.0) ; } Why so?

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• How to make a C program that can run x86 hex codes

  - by Iowa15

  I have an array of hex codes that translate into assembly instructions and I want to create program in C that can execute these. unsigned char rawData[5356] = { 0x4C, 0x01, 0x0A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x64, 0x0C, 0x00, 0x00, 0x3D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x01, 0x2E, 0x74, 0x65, 0x78, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xB4, 0x05, 0x00, 0x00, 0xA4, 0x01, 0x00, 0x00, 0x68, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x61, 0x00, 0x00, 0x00, 0x20, 0x00, 0x30, 0x60, 0x2E, 0x64, 0x61, 0x74, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x30, 0xC0, 0x2E, 0x62, 0x73, 0x73, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x30, 0xC0, 0x2F, 0x34, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00, 0x58, 0x07, 0x00, 0x00, 0x32, 0x0C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x20, 0x10, 0x30, 0x60, 0x2F, 0x33, 0x32, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00, 0x6C, 0x07, 0x00, 0x00,...and so on

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• What is a simple C library for a set of integer sets?

  - by conradlee

  I've got to modify a C program and I need to include a set of unsigned integer sets. That is, I have millions of sets of integers (each of these integer sets contains between 3 and 100 integers), and I need to store these in some structure, lets call it the directory, that can in logarithmic time tell me whether a given integer set already exists in the directory. The only operations that need to be defined on the directory is lookup and insert. This would be easy in languages with built-in support for useful data structures, but I'm a foreigner to C and looking around on Google did (surprisingly) not answer my question satisfactorily. This project looks about right: http://uthash.sourceforge.net/ but I would need to come up with my own hash key generator. This is a standard, simple problem, so I hope there is a standard and simple solution.

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• Printing factorial at compile time in C++

  - by user519882

  template<unsigned int n> struct Factorial { enum { value = n * Factorial<n-1>::value}; }; template<> struct Factorial<0> { enum {value = 1}; }; int main() { std::cout << Factorial<5>::value; std::cout << Factorial<10>::value; } above program computes factorial value during compile time. I want to print factorial value at compile time rather than at runtime using cout. How can we achive printing the factorial value at compile time? I am using VS2009. Thanks!

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• How to I count key collisions when using boost::unordered_map?

  - by Nikhil

  I have a data structure with 15 unsigned longs, I have defined a hash function using hash_combine as follows: friend std::size_t hash_value(const TUPLE15& given) { std::size_t seed = 0; boost::hash_combine(seed, val1); boost::hash_combine(seed, val2); ... return seed; } I insert a large number of values into a boost::unordered_map but the performance is not good enough. Probably, I could do better with an alternative hashing function. To confirm this, I need to check how many collisions I am getting. How do I do this?

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• Declaring a data type dynamically in C++

  - by Bobby

  I want to be able to do the following: I have an array of strings that contain data types: string DataTypeValues[20] = {"char", "unsigned char", "short", "int"}; Then later, I would like to create a variable of one of the data types at runtime. I won't know at compile time what the correct data type should be. So for example, if at runtime I determined a variable x needed to be of type int: DataTypeValues[3] x = 100; Obviously this won't work, so how could I do something like this?

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• How to prevent application thievery?

  - by Berdon Magnus

  Hey, I was wondering what the most effective way of preventing people from stealing my application (downloading a copy of the .apk online rather than buying it). I've spent a lot of time on one in particular (Droidbox) and won't be releasing Sync until I can guarantee that the people who are providing illegal copies of the pro version aren't able to. Anyone implemented this? I've tried checking my package signature verses an the signature of an unsigned copy but it appears to be the same - perhaps I'm doing something incorrectly here. I'm unsure whether people actually distribute the signed .apk in which case I don't think signature validation would work to begin with...

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• Possible compiler bug in MSVC12 (VS2013) with designated initializer

  - by diapir

  Using VS2013 Update 2, I've stumbled on some strange error message : // test.c int main(void) { struct foo { int i; float f; }; struct bar { unsigned u; struct foo foo; double d; }; struct foo some_foo = { .i = 1, .f = 2.0 }; struct bar some_bar = { .u = 3, // error C2440 : 'initializing' : cannot convert from 'foo' to 'int' .foo = some_foo, .d = 4.0 }; // Works fine some_bar.foo = some_foo; return 0; } Both GCC and Clang accept it. Am I missing something or does this piece of code exposes a compiler bug ? EDIT : Duplicate: Initializing struct within another struct using designated initializer causes compile error in Visual Studio 2013

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• JavaScript pack("d") - binary strings

  - by Tim Whitlock

  I'm trying to replicate the Perl and PHP style pack and unpack functions in JavaScript. Unsigned integers were easy enough, so my pack('n') and pack('N') are ok. But my lack of a computer science background is a hurdle now and I don't know where to start with pack('d') for packing JavaScript's standard floating point. Is there a JavaScript library for this out there? If not, is there a good resource where I can learn how to do this? I am fine with bitwise and binary level operations in JS, I just don't know where to start with the logic. Thanks.

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• How to default-initialize local variables of built-in types in C++?

  - by sharptooth

  How do I default-initialize a local variable of primitive type in C++? For example if a have a typedef: typedef unsigned char boolean;//that's Microsoft RPC runtime typedef I'd like to change the following line: boolean variable = 0; //initialize to some value to ensure reproduceable behavior retrieveValue( &variable ); // do actual job into something that would automagically default-initialize the variable - I don't need to assign a specific value to it, but instead I only need it to be intialized to the same value each time the program runs - the same stuff as with a constructor initializer list where I can have: struct Struct { int Value; Struct() : Value() {} }; and the Struct::Value will be default-initialized to the same value every time an instance is cinstructed, but I never write the actual value in the code. How can I get the same behavior for local variables?

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• What is the explanation for "warning: assuming that the loop is not infinite"

  - by James Morris

  I had just taken the decision to change as many variables from unsigned to int and upon recompiling the code in question, was greeted by this warning message: freespace_state.c:203: warning: assuming that the loop is not infinite The line in question: for (x = startx; x <= endx; ++x, ++xptr) This loop is 60 lines of code (inc white space/brackets etc), and has a goto within it, and at least one occurrence of continue. In this case, I think I am appreciative that GCC is assuming this loop is not infinite, because, it should never loop indefinitely. What is GCC trying to tell me here?

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• PHP and MySQL SELECT problem.

  - by R.I.P.coalMINERS

  Trying to check if a name is already stored in the database from the login user. The name is a set of dynamic arrays entered by the user threw a set of dynamic form fields added by the user. Can some show me how to check and see if the name is already entered by the login user? I know my code can't be right. Thanks! MySQL code. SELECT * FROM names WHERE name = '" . $_POST['name'] . "' AND userID = '$userID' Here is the MySQL table. CREATE TABLE names ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, userID INT NOT NULL, name VARCHAR(255) NOT NULL, meaning VARCHAR(255) NOT NULL, PRIMARY KEY (id) );

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• Convert hex to decimal keeping fractional part in Lua

  - by Zack Mulgrew

  Lua's tonumber function is nice but can only convert unsigned integers unless they are base 10. I have a situation where I have numbers like 01.4C that I would like to convert to decimal. I have a crummy solution: function split(str, pat) local t = {} local fpat = "(.-)" .. pat local last_end = 1 local s, e, cap = str:find(fpat, 1) while s do if s ~= 1 or cap ~= "" then table.insert(t,cap) end last_end = e+1 s, e, cap = str:find(fpat, last_end) end if last_end <= #str then cap = str:sub(last_end) table.insert(t, cap) end return t end -- taken from http://lua-users.org/wiki/SplitJoin function hex2dec(hexnum) local parts = split(hexnum, "[\.]") local sigpart = parts[1] local decpart = parts[2] sigpart = tonumber(sigpart, 16) decpart = tonumber(decpart, 16) / 256 return sigpart + decpart end print(hex2dec("01.4C")) -- output: 1.296875 I'd be interested in a better solution for this if there is one.

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• Unresolved External Symbol

  - by TomO

  I am working on wrapping a large number of .h and .lib files from native C++ to Managed C++ for eventual use as a referenced .dll in C#. I have the .lib files linked in and everything has been going smoothly so far. Upon wrapping the latest .h file, I hit a snag when 2 functions came back with the link error: error LNK2019: unresolved external symbol __imp__htonl@4 referenced in function "public: void __thiscall Field::setCharacter(unsigned char,int)" (?setCharacter@Field@@QAEXEH@Z) myutils.lib I have referenced "myutils.lib" in the linker options, so that shouldn't be the issue. What's strange is that I have about 20 functions in this particular .h file and all of the rest are linking just fine except for 3 functions. Any ideas?

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• Three boolean values saved in one tinyint

  - by Casper

  Hello, probably a simple question but I seem to be suffering from programmer's block. :) I have three boolean values: A, B, and C. I would like to save the state combination as an unsigned tinyint (max 255) into a database and be able to derive the states from the saved integer. Even though there are only a limited number of combinations, I would like to avoid hard-coding each state combination to a specific value (something like if A=true and B=true has the value 1). I tried to assign values to the variables so (A=1, B=2, C=3) and then adding, but I can't differentiate between A and B being true from i.e. only C being true. I am stumped but pretty sure that it is possible. Thanks

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• pointers in C with a #define

  - by milan

  The function: #define ASSOC(port) (*(volatile bit_field *) (&port)) The function call: #define SCLK ASSOC(PORTC).bit0 bit_field defined as a struct like this: typedef struct { unsigned char bit0 :1, bit1 :1, bit2 :1, bit3 :1, bit4 :1, bit5 :1, bit6 :1, bit7 :1; } bit_field; I don't know where &port is defined. Can someone please explain how the function is read and how it works please? I am not very good with pointers and this example in particular is very confusing with "*" in the front and at the end and the "&" with the port. Thank you

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• Is it a good idea to apply some basic macros to simplify code in a large project?

  - by DoctorT

  I've been working on a foundational c++ library for some time now, and there are a variety of ideas I've had that could really simplify the code writing and managing process. One of these is the concept of introducing some macros to help simplify statements that appear very often, but are a bit more complicated than should be necessary. For example, I've come up with this basic macro to simplify the most common type of for loop: #define loop(v,n) for(unsigned long v=0; v<n; ++v) This would enable you to replace those clunky for loops you see so much of: for (int i = 0, i < max_things; i++) With something much easier to write, and even slightly more efficient: loop (i, max_things) Is it a good idea to use conventions like this? Are there any problems you might run into with different types of compilers? Would it just be too confusing for someone unfamiliar with the macro(s)?

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• crc24 from c to python

  - by biiiiiaw

  can someone please translate this code to python? i have tried and tried again, but have not managed it: #define CRC24_INIT 0xB704CEL #define CRC24_POLY 0x1864CFBL typedef long crc24; crc24 crc_octets(unsigned char *octets, size_t len) { crc24 crc = CRC24_INIT; int i; while (len--) { crc ^= (*octets++) << 16; for (i = 0; i < 8; i++) { crc <<= 1; if (crc & 0x1000000) crc ^= CRC24_POLY; } } return crc & 0xFFFFFFL; } i have the rotate left function (ROL24(value,bits_to_rotate_by)), which i know works since i got it from a source code of a reputable programmer, but i dont get the * and ++ on octet. i only sort of understand how ++ works in c++, and i dont know what * is at all

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• Need to interface to a C++ DLL

  - by Pedro

  Hi, I need to call a C++ API from C#. I have been able to call the API, but the char[] parameters do not seem to be marshalling correctly. Here's the C++ signature: Create2ptModel(double modelPowers[2], double modelDacs[2], int pclRange[2], double targetPowers[32], double *dacAdjustFactor, unsigned short powerRampFactors[32], BOOL bPCLDacAdjusted[32], char calibrationModel[32], char errMsg[1024]) and this is how I am trying to call it from C# [DllImport("AlgorithmsLib.dll", EntryPoint = "_Create2ptModel@36", ExactSpelling = true, CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Auto)] private static extern AlgorithmStatus Create2ptModel( double[] modelPowers, double[] modelDacs, int[] pclRange, double[] targetPowers, ref double dacAdjustFactor, ushort[] powerRampFactors, bool[] bPCLDacAdjusted, /**/char[] calibrationModel, char[] errMsg/**/); Any idea of how I can marshall it correctly? Thanks in advance!

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