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• zeroing out memory

  - by robUK

  Hello, gcc 4.4.4 c89 I am just wondering what most c programmers do when they want to zero out memory. For example I have a buffer of 1024 bytes. Sometimes I do this: char buffer[1024] = {0}; Which will zero all bytes. However, should I declare like this and use memset? char buffer[1024]; . . memset(buffer, 0, sizeof(buffer); Is there any real reason you have to zero the memory? What is the worst that can happen by not doing it? Many thanks for any suggestions,

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• How to remove [^a-z\s] in C++

  - by Steven

  So far I have: int SimplifyText(char chars[], int length) { //To lower for(int i=0; i<length; i++) { chars[i] = tolower(chars[i]); } This function simplifies the text in the first argument which is an array containing the number of characters as given in the second argument The requirements are: tolower all remove all non-alpha characters replace multiple whitespace by one blank. Any leading whitespace at the beginning of the array should be removed completely. The resulting number of characters should be returned as the value of the function. And the annoying part: Another array cannot appear in the function Cannot use strings, only char arrays. Cannot using G++'s extension for setting an array size using a variable. Oh and can't use regex :) I'm stuck with this, any help would be great. :)

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• Using sizeof with a dynamically allocated array

  - by robUK

  Hello, gcc 4.4.1 c89 I have the following code snippet: #include <stdlib.h> #include <stdio.h> char *buffer = malloc(10240); /* Check for memory error */ if(!buffer) { fprintf(stderr, "Memory error\n"); return 1; } printf("sizeof(buffer) [ %d ]\n", sizeof(buffer)); However, the sizeof(buffer) always prints 4. I know that a char* is only 4 bytes. However, I have allocated the memory for 10kb. So shouldn't the size be 10240? I am wondering am I thinking right here? Many thanks for any suggestions,

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• Class basic operators

  - by swan

  Hi, Is it necessary to have a copy constructor, destructor and operator= in a class that have only static data member, no pointer class myClass{ int dm; public: myClass(){ dm = 1; } ~myClass(){ } // Is this line usefull ? myClass(const myClass& myObj){ // and that operator? this->dm = myObj.dm; } myClass& operator=(const myClass& myObj){ // and that one? if(this != &myObj){ this->dm = myObj.dm; } return *this; } }; I read that the compiler build one for us, so it is better to not have one (when we add a data member we have to update the operators)

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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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• How to access constant defined in child class?

  - by kavoir.com

  I saw this example from php.net: <?php class MyClass { const MY_CONST = "yonder"; public function __construct() { $c = get_class( $this ); echo $c::MY_CONST; } } class ChildClass extends MyClass { const MY_CONST = "bar"; } $x = new ChildClass(); // prints 'bar' $y = new MyClass(); // prints 'yonder' ?> But $c::MY_CONST is only recognized in version 5.3.0 or later. The class I'm writing may be distributed a lot. Basically, I have defined a constant in ChildClass and one of the functions in MyClass (father class) needs to use the constant. Any idea?

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• How to remove an item from a structure array in C++?

  - by Antik

  I have the following array structure (linked list): struct str_pair { char ip [50] ; char uri [50] ; str_pair *next ; } ; str_pair *item; I know to create a new item, I need to use item = new str_pair; However, I need to be able to loop through the array and delete a particular item. I have the looping part sorted. But how do I delete an item from an array of structures?

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• Evaluation of (de)reference operators

  - by Micha

  I have an (uncommented...) source file which I'm trying to understand. static const Map *gCurMap; static std::vector<Map> mapVec; then auto e = mapVec.end(); auto i = mapVec.begin(); while(i!=e) { // ... const Map *map = gCurMap = &(*(i++)); // ... } I don't understand what &(*(i++)) does. It does not compile when just using i++, but to me it looks the same, because I'm "incrementing" i, then I'm requesting the value at the given address and then I'm requesting the address of this value?!

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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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• explain this macro

  - by deostroll

  #define __T(x) L ## x Found in code from one of the MFC source header file. It is mostly used for converting strings to ........ (I don't know what). If I am correct it converts strings to LPCTSTR...don't know what that type is either... I can't seem to convert char* into LPCTSTR. While MFC file handling, the following code will always return error while trying to open the file... char* filepath = "C:\\Program Files\\Microsoft Office\\Office12\\BITMAPS\\STYLES\\GLOBE.WMF"; if( !file.Open((LPCTSTR)filepath , CFile::modeRead, &fexp) ) { fexp.ReportError(); return 1; } But instead if I wrote it this way, it doesn't give error: if( !file.Open( _T("C:\\Program Files\\Microsoft Office\\Office12\\BITMAPS\\STYLES\\GLOBE.WMF") , CFile::modeRead, &fexp) ) { fexp.ReportError(); return 1; } I am looking at passing a variable as the first argument to the CFile::Open() method.

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• Is there a good way to remove a character from a string without copying all the characters following

  - by piemesons

  I was given an interview question: // The first example: char text[] = "henri"; char *p; p = text; *(p + 1) = 'E'; // Output = hEnri // Now If we want to remove the "e" ie hnri, we would go for????? *(p + 1)=????? The obvious answer is to copy the rest of the array "back" one position. But this seems... unpleasant. Surely there is some better way?

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• does overload operator-> a compile time action?

  - by Brent

  when I tried to compile the code: struct S { void func2() {} }; class O { public: inline S* operator->() const; private: S* ses; }; inline S* O::operator->() const { return ses; } int main() { O object; object->func(); return 0; } there is a compile error reported: D:\code>g++ operatorp.cpp -S -o operatorp.exe operatorp.cpp: In function `int main()': operatorp.cpp:27: error: 'struct S' has no member named 'func' it seems that invoke the overloaded function of "operator-" is done during compile time? I'd add "-S" option for compile only.

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• Set argument pointer to point to new memory inside a function (without returning it) IN C

  - by user321605

  Hello, Hopefully my title was descriptive enough to attract the right help. I want to write a function that will return 1 thing, and modify a provided pointer in another. My current function declaration is . . . char * afterURL replaceURLS(char * body) What I want to do is copy all of body's data into a new string, and set body to point to this new data. I then want afterURL to point to a location within the new string. My issue is getting the actual pointer that is passed in to this function to point to the new data. Thanks in advance! Rob

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• C++ STL: Trouble with string iterators

  - by Rosarch

  I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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• syntax error : missing ';' before identifier

  - by numerical25

  I am new to c++, trying to debug the following line of code class cGameError { string m_errorText; public: cGameError( char *errorText ) { DP1("***\n*** [ERROR] cGameError thrown! text: [%s]\n***\n", errorText ); m_errorText = string( errorText ); } const char *GetText() { return m_errorText.c_str(); } }; enum eResult { resAllGood = 0, // function passed with flying colors resFalse = 1, // function worked and returns 'false' resFailed = –1, // function failed miserably resNotImpl = –2, // function has not been implemented resForceDWord = 0x7FFFFFFF }; This header file is included in the program as followed #include "string.h" #include "stdafx.h" #include "Chapter 01 MyVersion.h" #include "cGameError.h"

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• Read options from file

  - by Devel

  I would like to write a function which will read values from a text file and write them to variables. For example my file is: mysql_server localhost mysql_user root mysql_passworg pospaz mysql_database testgenerator log log.txt username admin password abcd and I have the same variables as the first word in the line. So how to make the function read data from file and do sth like this: char *mysql_server = localhost; char *mysql_user = root; ... I have no idea even how to start writing it...

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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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• Is it possible for a parent to use a child's constant or static variables from inside a static metho

  - by ryeguy

  Below is an example of what I'm trying to do. The parent can't access any of the child's variables. It doesn't matter what technique I use (static or constants), I just need some kind of functionality like this. class ParentClass { public static function staticFunc() { //both of these will throw a (static|const) not defined error echo self::$myStatic; echo self::MY_CONSTANT; } } class ChildClass extends ParentClass { const MY_CONSTANT = 1; public static $myStatic = 2; } ChildClass::staticFunc();

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• C++: use array of strings wrapped in namespace?

  - by John D.

  I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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• Redundant naming in C/C++ typedefs/structs

  - by bloomy

  #include <stdio.h> #include <string.h> const int NAMELEN=30; const int MAXCLASSSIZE=10; typedef struct StudentRec { char lastname[NAMELEN]; char firstname[NAMELEN]; long int ID; int finalmark; }Student; I'm new to coding..and I have a question about why there is Student; after the bracket.. is it a format that we have to follow.

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• C++: Throwing shared_ptr of derived and catching shared_ptr of base?

  - by hasvn

  Ok, I've been told this problem: Why can you throw a pointer to a derived class and catch a pointer to its base... but you can't do that with shared_ptrs? Example, this works: class Base {}; class Derived : public Base {}; int main() { try { throw new Derived() ; } catch( const Base2 * b ) { printf("Received a base" ) ; } return 0 ; } But this doesn't int main() { try { throw std::tr1::shared_ptr<Derived>( new Derived() ) ; } catch( const std::tr1::shared_ptr<Base> & b ) { printf("Received a base" ) ; } return 0 ; } Any ideas?

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• Returning objects with dynamic memory

  - by Caulibrot

  I'm having trouble figuring out a way to return an object (declared locally within the function) which has dynamic memory attached to it. The problem is the destructor, which runs and deletes the dynamic memory when the object goes out of scope, i.e. when I return it and want to use the data in the memory that has been deleted! I'm doing this for an overloaded addition operator. I'm trying to do something like: MyObj operator+( const MyObj& x, const MyObj& y ) { MyObj z; // code to add x and y and store in dynamic memory of z return z; } My destructor is simply: MyObj::~MyObj() { delete [] ptr; } Any suggestions would be much appreciated!

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• Singly-Linked Lists insert_back and isIncreasing

  - by rezivor

  I just finished writing a program that I can add, remove or print objects to a list, but I am having difficulty implementing two more functions that is insert_back, which inserts a value to the end of a list. Also,I have to modify the representation of a List and alter whatever methods are necessary to make insert_back run in constant time: O(1). This new operation should have the signature: void List::insert_back( const Object& data ); Also, isIncreasing, For example, for a list containing head-() (11) (8) (15) (3), isIncreasing() should return false. However, it would return true when working on a list containing head- () (7) (9) (15). This new operation should have the signature: bool List::isIncreasing() const; Thank you

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• Reading from a file into an array in c

  - by NaNa21

  My file contains a series of numbers (integer, float, integer, float ....), each written on a separate line. The numbers of columns are different from one line to another i.e. 1 2.45 3 1.75 5 3.45 7 2.55 9 3.25 6 1.75 4 3.55 6 2.55 9 2.45 The program should read the contents of the entire file and place the data into an array of type float with an entry for each line. Here is my basic solution, but this is only suitable if I have fixed no of columns. float Read(FILE *pFile) { char line[50]; char letter[5]; fi = fopen("file.txt", "r"); while (fgets(line,200,fi)!=NULL) { sscanf(line,"%f %f %f",&a[i], &a2[i],&a3[i]); printf("%2.0f %2.5f %2.0f\n",a[i],a2[i],a3[i]); } fclose(fi); return a[i]; } Please HELP.

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• extracting string occurrence in c

  - by David78

  I have a string from a text file that look something like this: long_str = "returns between paragraphs 20102/34.23" - 9203 1232 "test" "basic HTML" Note: Quotes are part of the string. int match(char *long_str){ char * str; if ((str = strchr(long_str, '"')) != NULL) str++; // last " ? else return 1; return 0; } Using strstr I'm trying to get the whole substring between the last two quotes: "basic HTML". I'm just not quite sure what would be a good and efficient way of getting that match. I'm open to any other ideas on how to approach this. Thanks

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