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• C++ : Initializing base class constant static variable with different value in derived class ?

  - by chmike

  I have a base class A with a constant static variable a. I need that instances of class B have a different value for the static variable a. How could this be achieved, preferably with static initialization ? class A { public: static const int a; }; const int A::a = 1; class B : public A { // ??? // How to set *a* to a value specific to instances of class B ? };

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• not working function with no errors

  - by aya

  hello.. I've implemented a function to display an avl tree after inserting nodes into it like this template void AVLtree::display() const { display(Proot); } template void AVLtree::display(Node * ptr) const { if(ptr==0) return ; cout<value<<" "; display(ptr-Pleft); display(ptr-Pright); } after compiling,there were no errors ,the program worked but nothing were printed on the screen help me please....!! thanks

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• Need help with displaying the message correctly in the pole display always starting at the beginning

  - by SA

  Hi, I am using an HP RS232 pole display with the following setting: Char type: USA/Europe (default) Command mode: EPSON (default) Baud rate: 9600, n , 8, 1 (default?) Passthru None (Default) Here's the code using System.IO.Ports; private SerialPort port; port = new SerialPort("COM2", 9600, Parity.None, 8, StopBits.One); port.Handshake = Handshake.None; Port.WriteLine("Welocome to something something"); It has 2 lines consisting of 20 characters each with a total of 40 characters. I have no control how and where the characters get displayed. I would like it to always begin on line 1 position 1 but as I said earlier how would I be able to do that. The same program if I run again and again it moves a character to the left. I have set it to accept ASCII char set and so I am able to type as is visble in the Writeline message

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• How can I declare a pointer with filled information in C++?

  - by chacham15

  typedef struct Pair_s { char *first; char *second; } Pair; Pair pairs[] = { {"foo", "bar"}, //this is fine {"bar", "baz"} }; typedef struct PairOfPairs_s { Pair *first; Pair *second; } PairOfPairs; PairOfPairs pops[] = { {{"foo", "bar"}, {"bar", "baz"}}, //How can i create an equivalent of this NEATLY {&pairs[0], &pairs[1]} //this is not considered neat (imagine trying to read a list of 30 of these) }; How can I achieve the above style declaration semantics?

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• What is wrong with my version of strchr?

  - by Eduard Saakashvili

  My assignment is to write my own version of strchr, yet it doesn't seem to work. Any advice would be much appreciated. Here it is: char *strchr (const char *s, int c) //we are looking for c on the string s { int dog; //This is the index on the string, initialized as 0 dog = 0; int point; //this is the pointer to the location given by the index point = &s[dog]; while ((s[dog] != c) && (s[dog] != '\0')) { //it keeps adding to dog until it stumbles upon either c or '\0' dog++; } if (s[dog]==c) { return point; //at this point, if this value is equal to c it returns the pointer to that location } else { return NULL; //if not, this means that c is not on the string } }

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• please help please

  - by davit-datuashvili

  http://stackoverflow.com/questions/2836934/how-to-compare-two-char-variables please show me a few steps how to start to write this code please

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• Best way to implement a data structure in PHP ?

  - by Double Gras

  Hi, I want to use some kind of data structure in PHP (5.2), mainly in order to not pollute the global namespace. I think about two approaches, using an array or a class. Could you tell me which approach is better ? Thanks $SQL_PARAMETERS = array ( 'server' => '127.0.0.1', 'login' => 'root'); class SqlParameters { const SERVER = '127.0.0.1'; const LOGIN = 'root'; } echo $SQL_PARAMETERS['server']; echo SqlParameters::SERVER;

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• How do I get characters common to two vectors in C++?

  - by Sam Phelps

  I am trying to compare two vector objects, and return a single vector containing all the chars which appear in both vectors. How would I go about this without writing some horribly complex manual method which compares every char in the first vector to every char in the second vector and using an if to add it to a third vector (which would be returned) if they match. Maybe my lack of real experience with vectors is making me imagine this will be harder than it really is, but I suspect there is some simplier way which I have been unable to find through searching.

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• Is there a simple script to convert C++ enum to string?

  - by Edu Felipe

  Suppose we have some named enums: enum MyEnum { FOO, BAR = 0x50 }; What I googled for is a script (any language) that scans all the headers in my project and generates a header with one function per enum. char* enum_to_string(MyEnum t); And a implementation with something like this: char* enum_to_string(MyEnum t){ switch(t){ case FOO: return "FOO"; case BAR: return "BAR"; default: return "INVALID ENUM"; } } The gotcha is really with typedefed enums, and unnamed C style enums. Does anybody know something for this? EDIT: The solution should not modify my source, except for the generated functions. The enums are in an API, so using the solutions proposed until now is just not an option.

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• How to check total cache size using a program

  - by user1888541

  so I'm having some trouble creating a program to measure cache size in C. I understand the basic concept of going about this but I'm still having trouble figuring out exactly what I am doing wrong. Basically, I create an array of varying length (going by power of 2s) and access each element in the array and put it in a dummy variable. I go through the array and do this around 1000 times to negate the "noise" that would otherwise occur if I only did it once to get an accurate measurement for time. Then, I look for the size that causes a big jump in access time. Unfortunately, this is where I am having my problem, I don't see this jump using my code and clearly I am doing something wrong. Another thing is that I used /proc/cpuinfo to check the cache and it said the size was 6114 but that was not a power of 2. I was told to go by powers of 2 to figure out the cache can anyone explain why this is? Here is the just of my code...I will post the rest if need be { struct timeval start; struct timeval end; // int n = 1; // change this to test different sizes int array_size = 1048576*n; // I'm trying to check the time "manually" first before creating a loop for the program to do it by itself this is why I have a separate "n" variable to increase the size char x = 0; int i =0, j=0; char *a; a =malloc(sizeof(char) * (array_size)); gettimeofday(&start,NULL); for(i=0; i<1000; i++) { for(j=0; j < array_size; j += 1) { x = a[j]; } } gettimeofday(&end,NULL); int timeTaken = (end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec *1000000 + start.tv_usec); printf("Time Taken: %d \n", timeTaken); printf("Average: %f \n", (double)timeTaken/((double)array_size); }

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• Dereferencing deleted pointers always result in an Access Violation ??

  - by m3rLinEz

  I have a very simple C++ code here: char *s = new char[100]; strcpy(s, "HELLO"); delete [] s; int n = strlen(s); If I run this code from Visual C++ 2008 by pressing F5 (Start Debugging,) this always result in crash (Access Violation.) However, starting this executable outside the IDE, or using the IDE's Ctrl+F5 (Start without Debugging) doesn't result in any crash. What could be the difference? I also want to know if it's possible to stably reproduce the Access Violation crash caused from accessing deleted area? Is this kind of crash rare in real-life?

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• Why isn't my IO executed in order?

  - by HaskellElephant

  Hi, I'm having some fun learning about the haskell IO. However in my recent exploration of it I have encountered some problems with IO not executing in order, even inside a do construct. In the following code I am just keeping track of what cards are left, where the card is a tuple of chars (one for suit and one for value) then the user is continously asked for wich cards have been played. I want the putStr to be executed between each input, and not at the very end like it is now. module Main where main = doLoop cards doLoop xs = do putStr $ show xs s <- getChar n <- getChar doLoop $ remove (s,n) xs suits = "SCDH" vals = "A23456789JQK" cards = [(s,n) | s <- suits, n <- vals] type Card = (Char,Char) remove :: Card -> [Card] -> [Card] remove card xs = filter (/= card) xs

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• Same loop giving different output. Java IO

  - by Nitesh Panchal

  Hi, I am facing a very strange problem where the same loop keeps giving me different different output on change of value of BUFFER final int BUFFER = 100; char[] charArr = new char[BUFFER]; StringBuffer objStringBuffer = new StringBuffer(); while (objBufferedReader.read(charArr, 0,BUFFER) != -1) { objStringBuffer.append(charArr); } objFileWriter.write(objStringBuffer.toString()); When i change BUFFER size to 500 it gives me a file of 7 kb when i change BUFFER size to 100000 it gives a file of 400 kb where the contents are repeated again and again. Please help. What should i do to prevent this?

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• Use C function in C++ program; "multiply-defined" error

  - by eom

  I am trying to use this code for the Porter stemming algorithm in a C++ program I've already written. I followed the instructions near the end of the file for using the code as a separate module. I created a file, stem.c, that ends after the definition and has extern int stem(char * p, int i, int j) ... It worked fine in Xcode but it does not work for me on Unix with gcc 4.1.1--strange because usually I have no problem moving between the two. I get the error ld: fatal: symbol `stem(char*, int, int)' is multiply-defined: (file /var/tmp//ccrWWlnb.o type=FUNC; file /var/tmp//cc6rUXka.o type=FUNC); ld: fatal: File processing errors. No output written to cluster I've looked online and it seems like there are many things I could have wrong, but I'm not sure what combination of a header file, extern "C", etc. would work.

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• Preprocessor directive to test if this is C or C++

  - by Collin

  I'm trying to find a standard macro which will test whether a header file is being compiled as C or as C++. The purpose of this is that the header may be included by either C or C++ code, and must behave slightly differently depending on which. Specifically: In C, I need this to be the code: extern size_t insert (const char*); In C++, I need this to be the code: extern "C" size_t insert (const char*); Additionally, is there a way to avoid putting #ifdef's around every declaration in the header?

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• java decmail string to AS 3.0 conversion procedure

  - by Jack Smith

  Hello, I have a problem with conversion java code to action script 3. Anyone can help with code translation? Thanks. public static short[] decmail_str_to_binary_data(String s) { short[] data = new short[s.length()/2]; for (int i = 0; i < s.length(); i += 2) { char c1 = s.charAt(i); char c2 = s.charAt(i + 1); int comb = Character.digit(c1, 16) & 0xff; comb <<= 4; comb += Character.digit(c2, 16) & 0xff; data[i/2] = (short)comb; } return data; }

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• Strange exception phenomenon in Windows 7

  - by Level 2

  I spot some interesting articles about exception handle in CodeProject http://www.codeproject.com/KB/cpp/seexception.aspx After reading, I decided to do some experiment. The first time I try to execute the following code char *p; p[0] = 0; The program died without question. But After several times when I executed the same problem binary code, it magically did fine. Even the following code is doing well. Any clue or explanation? char *p p[1000] = 'd'; cout<<p[1000]<<endl; My O/S is Windows 7 64bit and compiler is VS2008 rc1.

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• Loading Unmanaged C++ in C#. Error Attempted to read or write protected memory

  - by Thatoneguy

  I have a C++ function that looks like this __declspec(dllexport) int ___stdcall RegisterPerson(char const * const szName) { std::string copyName( szName ); // Assign name to a google protocol buffer object // Psuedo code follows.. Protobuf::Person person; person->set_name(copyName); // Error Occurs here... std::cerr << person->DebugString() << std::endl; } The corresponding C# code looks like this... [DllImport(@"MyLibrary.dll", SetLastError = true)] public static unsafe extern int RegisterPerson([MarshalAs(UnmanagedType.LPTStr)]string szName) Not sure why this is not working. My C++ library is compiled as Multi Threaded DLL with MultiByte encoding. Any help would be appreciated. I saw this is a common problem online but no answers lead me to a solution for my problem.

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• Basic C++ code for multiplication of 2 matrix or vectors (C++ beginner)

  - by Ice

  I am a new C++ user and I am also doing a major in Maths so thought I would try implement a simple calculator. I got some code off the internet and now I just need help to multiply elements of 2 matrices or vectors. Matrixf multiply(Matrixf const& left, Matrixf const& right) { // error check if (left.ncols() != right.nrows()) { throw std::runtime_error("Unable to multiply: matrix dimensions not agree."); } /* I have all the other part of the code for matrix*/ /** Now I am not sure how to implement multiplication of vector or matrix.**/ Matrixf ret(1, 1); return ret; }

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• Casting a Calculated Column in a MySQL view.

  - by Chris Brent

  I have a view that contains a calculated column. Is there are a way to cast it as a CHAR or VARCHAR rather than a VARBINARY ? Obviously, I have tried using CAST(... as CHAR) but it gives an error. Here is a simple replicable example. CREATE VIEW view_example AS SELECT concat_ws('_', lpad(9, 3,'0'), lpad(1,3,'0'), date_format(now(),'%Y%m%d%H%i%S')) AS calculated_field_id; This is how my view is created: describe view_example; +---------------------+---------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------------+---------------+------+-----+---------+-------+ | calculated_field_id | varbinary(27) | YES | | NULL | | +---------------------+---------------+------+-----+---------+-------+ select version(); +-----------------------+ | version() | +-----------------------+ | 5.0.51a-community-log | +-----------------------+

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• Is it good practice to initialize array in C/C++?

  - by sand

  I recently encountered a case where I need to compare two files (golden and expected) for verification of test results and even though the data written to both the files were same, the files does not match. On further investigation, I found that there is a structure which contains some integers and a char array of 64 bytes, and not all the bytes of char array were getting used in most of the cases and unused fields from the array contain random data and that was causing the mismatch. This brought me ask the question whether it is good practice to initialize the array in C/C++ as well, as it is done in Java?

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• Why this works (Templates, SFINAE). C++

  - by atch

  Hi guys, reffering to yesterday's post, this woke me up this morning. Why this actually works? As long as the fnc test is concerned this fnc has no body so how can perform anything? Why and how this works? I'm REALLY interested to see your answers. template<typename T> class IsClassT { private: typedef char One; typedef struct { char a[2]; } Two; template<typename C> static One test(int C::*); //NO BODY HERE template<typename C> static Two test(…); //NOR HERE public: enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1 }; enum { No = !Yes }; }; Thanks in advance with help to understand this very interesting fenomena.

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• jquery ui autcomplete does not disapper with no result

  - by mike

  Hi, I'm using jquery ui autocomplete with the following code: $('#company').autocomplete({ source: function(request, response) { var company_name = $('#company').val(); $.ajax({ type: 'post', url: 'http://new.admin.localhost/client/helper/lookup_company_name', cache: false, data: { company : company_name }, dataType: 'json', success: function(data) { //alert(data); response($.map(data.companies, function(item) { return { label: item.company, value: item.company } })) } }) }, minLength: 2, }); This works as expected... The problem is, if the first few chars match something and then you enter a char that should "break" any match, it just keeps the drop down in place with the results for the last matched char... make sense? Would this be something I needed to change in the script that returns the data or something in the jquery? thanks!

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• strenge exception phenomenon in win7

  - by Level 2

  Hello all, I spot some interesting artcles about exception handle in codeproject http://www.codeproject.com/KB/cpp/seexception.aspx after reading, I decided to do some experiment. The first time I try to excute the following code char *p; p[0] = 0; The program died without question. But After serveral time I execute the same problem binary code. It magically did fine. even the following code is doing well. any clue or explain? char *p p[1000] = 'd'; cout<<p[1000]<<endl; my os is windows 7 64bit and compiler is vs2008 rc1.

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• How can I remove the head of a main function?

  - by Nathan McDavitt-Van Fleet

  I am trying to move some code from a seperate binary and have it inside my main program. Unfortunately I can't mimic the initialization variables for the main function. How can I create argc and argv by hand? Can someone give me some example assignments. since it looks like this: int main(int argc, char *argv[]) I figured I could assign them like this: int argc=1; char *argv[0]="Example"; But it doesn't work. Can anyone tell me how this might be done?

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