C++ :: Map Comparison Fails In Function Const
Jan 27, 2012
Why I'm getting an error here. I've dumbed down my code for simplicity and removed irrelevant code.
PHP Code:
class Foo {
public:
bool IsNull() const;
private:
std::map<int, int*> test;
[Code] ....
I'm getting a "passing...discards qualifiers" error on my if statement and not sure why because I'm not changing anything. I know removing const or making test mutable fixes the issue. I've been taught to always make a function const if it doesn't change anything, in which case, have I finally come across an acceptable time to use mutable?
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Nov 3, 2013
What I have is a main function that takes input characters from the command prompt during the main function call, and coverts it to an integer array a using atoi. (starting at the 2nd character - the 1st is reserved for another call that I plan to reference later, and the 0th is obviously the ./function). A function is then called to find the mode of an array (the range of values in the array is 1-30). Now, when I run the whole thing, I get a segmentation fault (core dumped) for even number of arguments. It's late and I've been staring at it for too long...
Code:
#include <stdio.h>
#include <stdlib.h>
int get_mode(int a[], int count);
[Code]......
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Apr 13, 2014
I have a quick question about dynamic memory. I know that if you are dynamically allocating memory for a single data array and it fails, you can immediately abort the program via a return statement, but is this also true with multiple data arrays? For instance:
int *foo, *bar
foo = new (nothrow) int [5];
bar = new (nothrow) int [5];
if (foo == nullptr || bar == nullptr)
return -1;
else
/*rest of execution */
If the answer to the previous question is no, do you need to do a delete[] on the arrays that succeeded before terminating the application? Say foo is correctly allocated but bar fails, would you have to do something like this?
int *foo, *bar
foo = new (nothrow) int [5];
bar = new (nothrow) int [5];
if (foo == nullptr || bar == nullptr) {
if (foo == nullptr && bar != nullptr)
delete[] bar;
[Code] .....
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Apr 29, 2014
I have a very strange problem with the system() function (on XP).
I have the following code:
Code:
char *text1 = ""A SpaceAction.bat" fred";
char *text2 = ""A SpaceAction.bat" "fred"";
int main(int argc, char *argv[]) {
printf("%s
", text1);
[Code] .....
When I run it where "A Space" is a directory with a space in the name, this is the result:
Code:
"A SpaceAction.bat" fred
F:Test>echo Testing
Testing
"A SpaceAction.bat" "fred"
'A' is not recognized as an internal or external command, operable program or batch file.
It seems that the double quotes round an argument make the parsing of the command fail.
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Nov 6, 2013
I think that the getpixel function (existed in sdl documentation) gets the color of the coordinate indicated by x and y
Uint32 getpixel(SDL_Surface *surface, int x, int y) {
int bpp = surface->format->BytesPerPixel;
/* Here p is the address to the pixel we want to retrieve */
Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
switch(bpp) {
[Code]...
my problem is that, I want to compare it with the white/black color ,so how can I do that?
I tried this way but it does not work
int main(int argc,char *argv[]) {
SDL_Init(SDL_INIT_VIDEO);
SDL_Surface *screen = SDL_SetVideoMode(600,400,32,SDL_HWSURFACE|SDL_DOUBLEBUF);
SDL_Event event;
bool pass = true;
SDL_Color color = {0,0,0};/// Black color
if(color==getpixel(screen,0,0)
[Code]...
the error C:Documents and SettingsTechno01Bureausdlmain.cpp|83|error: no match for 'operator==' in 'color == getpixel(screen, 0, 0)'|
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May 5, 2014
I'm trying to write a function called 'set' that sets the value of the i'th cell to val on my linkedList, and then returns the previous contents. I am stuck on it due to compiling errors:
This is my Node struct:
#ifndef NODE_H
#define NODE_H
#include <iostream>
template <typename T>
struct Node {
friend std::ostream &operator <<(std::ostream &os, const Node<T> &node) {
[Code] ....
The following is my set function:
template <typename T>
T set(Node<T> *head, int i, const T &val) {
for(int n = 0; n < i; n++)
if(head == val) {
val = i;
} return val;
} #endif
When I try to call it in the main() I get these errors:
node_utils.h: In function ‘T set(Node<T>*, int, const T&) [with T = int]’:
node_demo.cpp:26:38: instantiated from here
node_utils.h:161:2: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
node_utils.h:162:3: error: assignment of read-only reference ‘val’
So, I understand that I can't compare head & val on my if-statement -- But what do I do?
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Jun 7, 2013
Now I am stuck with getting const char* array from function to main.
Code:
const char* values[3];
strings_to_array()
printf("%s
", values[1]);
printf("%s
", values[2]); function: Code:
const char* strings_to_array()
}
[code]....
First, I cant get strings printed out in main.
Second, is here way to get number of such elements which array contains like higher languages have "count" or "ubound" or such?
Third, next function which need that array assumes that array of const chars* is 1 based. Can that be set in C or here are allways zero based arrays?
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Sep 27, 2014
i am trying to describe the unusual situation where you declare a class member function with this format:
bool class::function_name(void) const
Specifically where the 'const' follows the parameter list. It is my understanding this is a very useful way of ensuring that whatever code you put in the function definition cannot change any data members of its class.
However I have recently read that this form of declaration should not be used as it leads to less optimized and slower code. Is this correct?
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Oct 5, 2013
Are there other ways of calling a const/non-const override? I want to defined some functions in terms of others, particularly accessors which might or might not require constness- in order to not copy & paste code. This is my current solution:
struct dumbArray {
dumbArray(unsigned int size):
m_array(new int[size]){
}
~dumbArray(){
delete m_array;
[Code] .....
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Dec 7, 2013
difference between const and static const, more effectively. I know the basic concept of const and static but I need clear explanation of declaring "const" and "static const"
Ex:
const int a;
static const int a;
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Jun 19, 2013
Is there any way to cast a non-const variable to const one?
I want to read variable n from file and then use it to declare array "int arr[n]", but because n is non-const, the compiler doesn't allow me to do that.
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Apr 21, 2014
I am trying use a print function to print out data in a struct. My questions are:
1. I have to use pass by reference. For the print function, I am passing the struct pointer as a reference, however, I don't want the print function to accidentally change anything. How can I make it use const to ensure that?
2. The deleteprt function doesn't look right to me. I feel like it should just be delete ptr not delete [] ptr.
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <string>
using namespace std;
struct Inventory {
[Code] .....
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Sep 30, 2013
I am a newbie to C++ and VS ++. I have created a windows form application by dragging and dropping button, label..etc. i wish label text to be appeared as return value from a function. The function returns ' const char* '.how this returned string pointer can be used to display label text.?
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Jul 13, 2013
So I start thinking about what's the difference between this 2 code
map<const int, float> map_data;
map<int, float> map_data;
But it seems I can't find the difference, is there any difference between this 2 code ?
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Jan 12, 2015
I`ve wrote a function for my utility to XOR char* buffer by a key, then to reverse it with the same key. Here is the code, it`s simple enough:
Code:
static inline char* XOR_buffer(const char* d, const char* k ) {
char *newstr = (char*) malloc(sizeof(char)* strlen(d));
newstr[0]='';
printf("%d is size of string
", strlen(d));
char *begin = newstr;
char* ret = begin;
int len = strlen(k);
}
[code]....
The lengh of the string is reduced by the second XOR call. You can try it out, just define XORDBG to view the error message in the second pass to the buffer.
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May 29, 2013
i created an com client that try to create com server with the command CreateInstance. at win 7 it works fine (both 32 and 64 bit). but with xp it fails. i created the app with win 7 - 64 bit.
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Oct 6, 2014
cin returns fail on trying to read double value.
Code:
#include<iostream>
#include<array>
using namespace std;
const int MAX = 10;
void read_donations(array<double, MAX>& a, int& count);
int main()
[Code] ....
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Jan 2, 2015
I am creating a special struct with unknown functions. I use this approach:
Callbacks.h Code: #ifndef CALLBACKS
#define CALLBACKS
struct Callbacks;
struct Callbacks* getNewCallback();
[Code]....
When I ran it only the calls from doers array is called 7 times normally, and donters only one time. Why is that? When I call doers from the second loop, it prints the doers functions again....and only one call to donters is made to the first static inline donter functions __dont1()...
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Mar 29, 2014
I'm trying to write a piece of code that calculates the difference in days between two manually input dates. The part of my code that's causing problems is:
xxx
When running the code and prompted to enter the date, if I input for example 31/12/2014, it'll be rejected and send me back to the beginning of the loop. Any date with 31 days involving months 1, 3, 5, 7, 8, 10 or 12 causes this problem. All other valid dates however work perfectly fine (e.g. 30/4/2014).
Something possibly worth mentioning is that, when I take out all other conditions from the loop, i.e.
xxx
it works fine (31/12/2014 is accepted), but of course I need all of the other conditions in there too.
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Jan 25, 2015
So the question is this [URL] .....
My code is this:
#include <iostream>
#include<cmath>
using namespace std;
int main(int argc, char *argv[]) {
long double div;
//div=((1e+9)+7);
[Code] .....
The problem is when the hackerrank inputs the following:
10
5351871996120528
2248813659738258
2494359640703601
6044763399160734
3271269997212342
4276346434761561
2372239019637533
5624204919070546
9493965694520825
8629828692375133
My code gives the wrong output.
The output is supposed to be
578351320
404664464
20752136
999516029
743537718
323730244
174995256
593331567
136582381
305527433
So what changes should I make to get my code give the correct output.
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Feb 4, 2015
I'm trying to write a wrapper for rapidXML in order to use it in my projects however I've run into a curious bug that's preventing me from properly saving the XML documents I'm working with. The gist of it is: simply parsing a very simple xml doc and then saving the same document to the same file (without modifying it) creates a mostly correct output except for scrambling a few node closures:
bool rXMLwrapper::parse(){
try{
std::ifstream file(filepath.c_str());
if(!file.is_open()){throw std::bad_alloc();}
std::stringstream buffer;
buffer << file.rdbuf();
file.close();
[code]....
I'm using this patch for rapidXML: [URL]
As a foot note: I'm almost certain it's not an issue with the parse() function.
If I parse() the document and then call std::cout<<doc; it prints the document perfectly fine to the console, but for some reason std::ofstream<<doc; causes issues.
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May 17, 2014
The code is supposed to display the total and averages of the data as well, but cuts off due to an error in the code. The code should also:
1)Print checks for all employees, one per page, sorted by lastname. The first check number, 100, is to be read from a company data file (see requirement 4). The border of each check is important and should not be omitted.
2)Convert the net pay to a text string for each check printed.
3)Print a reference code on each check. The reference code is obtained by combining the first letter of the lastname with all the consonants remaining after removing all vowels (a,e,i,o,u).
4)Use the same employee data found in assignment 2. Use the following company data, obtained from a text file,
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
[code]....
And here's where the program stops. URL.....
Output I'm expecting: Program to display totals and averages (worked before I turned everything into an array), now exits with error before totals/averages are displayed. Program also writes up a report.txt file that also writes this information into it, as well as using a quicksort to organize the names alphabetically, and print paychecks (all of the #BORDER, #HEADER1-8, #STUB, etc). In that check a reference code is also generated (teacher gave us code, we just had to modify for our final program as seen here)
Flow of the program: Print headings to label all of the input data we will enter soon under the categories as listed in the heading. Initialize all of our totals (in our array) to value of 0. These will be added in a loop "AddAccumulators" which takes our value for the hours, payrate, and taxes from each employee array structure and adds it to the total array. Program will write this information into the report.txt file with the HEADER line for totals, and should be displaying it in that picture. (Same for averages). After all of the data is calculated, the Reference code, Totals, Averages, and individual employee data is taken and put into printing out a Check Header and Stub.
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Dec 9, 2013
How do i display the output ? This program only saves the output to "gpa.txt" I want it to also display the output to cmd.
#include <iostream>
#include <iomanip>
#include <fstream>
#include <cmath>
#include <string>
using namespace std;
const int SIZE = 10;
[Code] ....
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Jun 23, 2014
I have this proxy class generated from a webservice:
/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("System.Xml", "4.0.30319.18408")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="java:se.atg.aisbean.calendar")]
public partial class RaceDayCalendarSimple : object, System.ComponentModel.INotifyPropertyChanged {
[Code] ....
I'm trying to access this method "RaceDaySimple[] raceDay" and display it on "WebForm1.aspx":
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="WebServiceClient.WebForm1" %>
<!DOCTYPE html>
[Code] ....
So on "WebForm1.aspx.cs" I'm trying to access the method "RaceDaySimple[] raceDay" and display it inside the div "test":
test.InnerHtml = pbs.fetchRaceDayCalendarSimple().raceDay;
But I'm getting the error:
Cannot implicitly convert 'WebServiceClient.InformationServiceReference.RaceDaySimple[]' to 'String'
So how do I acces this method proparly and display the content on "WebForm1.aspx" inside the div "test"?
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Dec 27, 2012
I have some problem while allocating memory to a union inside structure. Below is the code i am using
ON SYSTEM1:
This works fine
ON SYSTEM2:
compiler complains saying "need structure or union type" while allocating MYSTRUCT1.
If I change:
shreyas[0].UnionAttr.struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)
to
shreyas[0].UnionAttr->struct1 = (MYSTRUCT1 *) malloc (sizeof(MYSTRUCT1)
This compiler on SYSTEM2 is happy. but second way does not look correct to me and compiler on system 1 complains about it. Which is the correct way to allocate memory?
If first one is correct then what should i look in for to avoid this error? Could this be an issue with compiler on SYSTEM2? If i use second method on SYSTEM2 code segfaults during malloc.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct mystruct1 {
int a;
int b;
[Code] ....
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Jan 24, 2014
Background: I'm using SDL and CodeBlocks and trying to make a Graphics class that would simplify some SDL operations such as drawing and loading images.
Issue: The loadImage function in the graphics class fails to load the image correctly and so the program prints out a blank window during run-time. I've tried multiple ways of passing a string literal into the function the surface temp fails to load and so background in Game fails to load. After testing it several times, I'm pretty sure that the issue lies with SDL_LoadBMP not registering the passed variable for whatever reason. I know the image is in the right place as writing SDL_LoadBMP("./Graphics/image.bmp"); brings it up just fine.
Current Code:
Main simply creates a Game object and execute(), so I didn't feel the need to put it on here.
Game.h
#ifndef GAME_H
#define GAME_H
#include "SDL/SDL.h"
#include "SDL/SDL_ttf.h"
#include "Graphics.h"
#include <string>
#include <cstring>
using namespace std;
//GLOBAL CONSTANTS
//game window settings
[Code] ....
Output: A blank window. (It should show the background image but doesn't.)
Note: I originally wrote it as gfx.loadImage(background, "./Graphics/image.bmp") but that gives me a conversion warning and still fails to show the image when the program runs. I've tried looking up examples similar to what I was doing but no one else seems to have this problem.
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