C++ :: Declaring Pointers Vs Regular Variables?
Aug 9, 2013
I really do not see the difference between these two declarations:
int myvariable;
int * mypointer;
It is said that when you define a pointer, instead of containing actual data, it contains a pointer to the memory location where information can be found.
But doesn't the other variable declaration do the same? It obviously doesn't have data either. And it must be stored in a memory location as well. So I do not see the difference.
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Nov 12, 2012
This is a c program that is failing to compile. The error occurs in the calcLabs() function. The error called out is (btw, I'm using VS 2010): Error4error C2143: syntax error : missing ';' before 'type'
I don't understand why the compiler is not letting me declare variables in the calcLabs() function!
Code:
#include<stdio.h>
#include<stdlib.h>
void calcPercent(double *);
double calcLabs();
double calcExams();
double calcFinal();
char calcLetter(float);
[code]...
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Jan 22, 2014
I am looking for a way to declare variables at run time which being a static language shouldn't happen. I will explain my situation.
I am upgrading a legacy program that modifies executables (non malicious). I am trying to add 64bit support.
It is a huge project and I understand the majority of it but my issues with how it handles the input data.
It has a struct that certain parameters of the input file is loaded into:
Code:
typedef struct DATA {
DWORD Size;
IMAGE_NT_HEADERS32 Headers;
} _DATA; *PDATA
etc, etc its a huge list.
My problem lies in the fact that I need to change IMAGE_NT_HEADERS_32 to IMAGE_NT_HEADERS64 at runtime.
That DATA struct gets called at least 110 times during runtime.
How I might tackle this? Having a conditional statement repeated that many times seems ridiculous.
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Sep 30, 2014
I have created a windows form project in visual studio so that I can use a windows form to interact with the game class that I'm creating, but I'm running into some problems.
For one thing, I would like to be able to call Image::FromFile() one time only during initialization, and store the result in a member variable (called mBGImage). From what I can tell, the variable needs to be of type String^ (this caret symbol is new to me, but I understand it is the "managed code" version of the standard pointer, which would look like String*).
When I try to compile the following code (located in my header file) I get the error :
"error C3265: cannot declare a managed 'mBGImage' in an unmanaged 'BSG::BSGame'".
How can I store the result of Image::FromFile() permanently in my class?
When I try to declare a global variable of type "Image^", I get "error C3145: global or static variable may not have managed type System:rawing::Image ^"
#include "stdafx.h"
using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
[Code] ......
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May 24, 2013
I am having following pointer variable declaration
Code: Static double (*funcs[]) (double) = { sin,cos,tan,asin,acos};
Here funcs is an array of pointers to functions which take double as input and gives double as output with static as storage type am I right.
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Oct 15, 2014
I have made an application and I have basically solved everything. But the only problem is that I am using global variables because it felt like the smoothest, so my program is built on it.
But now I've read around and I understand that you should not use these(?). Do you think pointers is the best think to use instead?I have previously declared my board array and some variables as global and I want them in alot of functions.I have read and understand the procedure for the use of pointers so I can use my int's in the other functions by doing like this? Code: #include <stdio.h>
int justprint();
int main()
{
int Row = 2;
int Column = 2;
int *pRow = &Row;
int *pColumn = &Column;
[code]...
But how do I do it with an array like this one? If I declare it in the main function, and then want to use it in other functions.Or are there better, easier solutions?
Code: char game[3][3]={{0,0}};
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Mar 26, 2013
The following function uses reference variables as parameters. Rewrite the function so it uses pointers instead of reference variables, and then demonstrate the function in a complete program.
int doSomething(int &x, int &y)
{
int temp =x;
x = y * 10;
y = temp * 10;
return x + y;
}
I understand how to covert the reference variables to pointers, however I am stuck on this error. Either I get the error listed in the title or (with a few changes) the error "invalid conversion from 'int' to 'int*'"
What am I doing incorrectly?
#include <iostream>
using namespace std;
int doSomething(int*, int*);
int main(){
int X, Y, result;
[Code] ....
I have multiplied both x and y by 10 and then added them together!
Here is the result " //I really didn't know how else to use the "doSomething" function in a meaningful way. So... I just stated what the function does.
<< result << ".
";
system("PAUSE");
return 0;
}
int doSomthing(int *x, int *y)
[Code] .....
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Apr 23, 2013
I have the following code. According to this the values of pointers p[0] and p[1] remains unchanged since the swap is made to local variables in swap function.Now my doubt is how can I swap the pointers p[0] and p[1] inside the function swap??
Code:
#include<stdio.h>int main(){char*p[2]={"hello","good morning"};
swap(p[0],p[1]);
printf("%s %s",p[0],p[1]);return0;
}void swap(char*a,char*b){char*t; t=a; a=b; b=t;
}
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Feb 28, 2014
Which is more efficient in functions? Returning values or using pointers to redefine variables passed as arguments?
I mean either using:
void ptr_Func(int *x)
{
*x = *x+1
}
or
int ptr_Func(int x)
{
return x + 1;
}
In terms of speed, memory use etc.I want to know general efficiency, I know it will obviously vary with different uses and circumstances.
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Oct 23, 2013
I am trying to create a NFA from a regular expression. I have a grasp on reading in the regular expression and being able to make a stack from it. The part I am struggling on is mapping the characters in the regular expression to an integer indicating the variables order in the expression. I am just not sure how to go about this.
My code so far...
Code:
#include<stdio.h>
#include<stdlib.h>
#include "stack.h"
int main(void)
{
char expression[80];//array to store regular expression
[Code] .....
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Aug 25, 2014
I have this bit of code that I found here: [URL] and at first regex would work, but then when I hit "[]" it wouldn't. Here's the code:
#include <iostream>
#include <string>
#include <regex>
[Code]....
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Jun 26, 2013
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
int main () {
[Code] ....
I'm not sure why my loop isn't running right. I've also used if/if and if/else . Nothing worked
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Sep 5, 2013
So I need to use boost/regex for regular expressions. someone told me that it needs to be built. the first problem is boost doesn't tell you how to build it and the second is i did sudo apt-get install libboost something. I don't remember the exact name of the package. it installed but i dont know how i would build it when its installed.
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Dec 11, 2013
writing a program for "Validating the e-mail id without using regular expressions in c/c++"?
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May 22, 2014
In order to parse mathematical expressions I am trying regular expressions and a recursive algorithm, but I have a problem with the four basic operations: +, -, *, /.
Trying to analyze a string like "a+(b+c)", if I use the pattern for a sum "(.+)+(.+)" the program matches it recognizing as subpatterns: "a+(b" and "c". How could I achieve the program to try also the other possibility?
I think that it would be great something like an regex_iterator which worked with regex_match instead of regex_search. I mean, an iterator that iterates over all the possible ways to match a given regular expression and a given string. This way I could loop through all these possibilities until the two subpatterns produced were correct mathematical expressions.
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Aug 22, 2013
Its a code in module of my program, where I need to print current time (HH:MM:SS) at regular intervals.
Code:
#include<time.h>
#include<stdio.h>
//#include<windows.h>
void delay(unsigned int t){ // loop for some delay.
[Code] ....
But when I am running this code I expect this to print difference in time due to delay. But it doesn't enter the delay loop, why ?
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Apr 9, 2012
<IMG border=0 alt="UserDeviceId = 70813215">
Above is the sample string object from this i need to find the integer value of UserDeviceId.
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Jan 5, 2015
I have programmed a program for billing system. I have used parameters and arrays. All the functions are working except a one function. (Regular package function).
#include <iostream>
#include <fstream>
#include <string>
#include <ctime>
using namespace std;
void main(int &minutes, int &minutesd,int &minutesn) {
[Code] .....
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Mar 14, 2014
I have an EDI file whose structure is given below. This file has multiple records, each record contains a header (e.g EDI.DD.0000000001.20130809), then contents (i.e multiple paragraphs of text) and then footer (e.g End of Report/No EDI Activity). I have to read that entire file using regular expression using three groups.
I am using following regular expression to read the file.
(?<header>[A-Z]{3}.[A-Z]{2}.[0-9]{10}.[0-9]{8}) | (?<footer> (EndsofsReport|NosEDIsActivity)) |
(?<content>(?<=k<header>).*(?=k<footer>))
That expression reads the "header" and "footer" in respective groups properly but didn't pick the contents between header and footer in "contents" group.
I have changed the font of header and footer in below file to understand the format. I am using asp.net 3.5 framework.
//------------------Start of EDI File---------------------//
EDI.DD.0000000001.20130809
ORIGINATOR INFORMATION Company Name: UNITED HEALTHCAR Identification: 9024125001 Originating DFI: 002100002
RECEIVER INFORMATION Receiver Name: HEALTH & WELLNESS DFI Account Number: 0000000000000001 Receiving DFI ID: 434343430 ID Number: Transaction Type: 22 Deposit
ORIGINATOR INFORMATION Company Nam
[Code] ....
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Jan 17, 2015
lets say we have a valid class with full implementation, X. can this class be declared as forward in Y header file:
Code: class X;
class Y{
X* m_X;
}
but still be used as regular in the cpp file?
Code:
#include "Y.h"
#incldue "X.h"
T Y::function(){
m_X->doSomething();
}
visual studio prevents me from doing it , I wonder if the standard also says so.
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Feb 28, 2014
I'm trying to create an array of pointers to pointers which will point to array of pointers (to strings) I tried
Code:
int i;
char *string[]={
"my name is dave",
"we like to dance together",
"sunny day",
"hello",
[code]...
the app keeps crashing , I don't know how to make the array-elements to point to another array-elements..
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May 21, 2013
I am a little confused while comparing char pointers to integer pointers. Here is the problem:
Consider the following statement;
char *ptr = "Hello";
char cArr[] = "Hello";
When I do cout << ptr; it prints Hello, same is the case with the statement
cout << cArr;
As ptr and cArr are pointers, they should print addresses rather than contents, but if I have an interger array i.e.
int iArr[] = {1, 2, 3};
If I cout << iArr; it displays the expected result(i.e. prints address) but pointers to character array while outputting doesn't show the address but shows the contents, Why??
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Nov 6, 2014
I am putting a instance o the Vehicle Class inside the constructor of the Calculate Class then calling it later. I get a warning saying the variable is not used and a error when I try to used the functions from the vehicle class saying use of undeclared identifier.
Code:
#include <iostream>
#include "Calculate.h"
#include "Vehicle.h"
#include <fstream>
Calculate::Calculate(){
[Code] ....
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Jun 5, 2013
I am a bit confused about how specific one must be with arguments when declaring a function. I'll show you two functions from the book I'm using to learn C to show you what I mean.
Example 1 (greatest common denominator function):
Code:
void gcd (int u, int v) {
int temp;
printf ( "
[Code] ....
So in that function, there are exactly two arguments, because that's how many arguments the algorithm to find the gcd takes. No problem there, makes sense to me. Then further in the chapter on functions I run into this,
Example 2 (square root function):
Code:
float absoluteValue (float x) {
if ( x < 0 )
x = -x;
return x;
[Code] ....
In this second example, we have a square root function that is preceded by an absolute value function. The absolute value function has the one argument, "float x", however when this function is called within the square root function, the arguments "guess * guess * -x" are passed to it. I'm confused how this absolute value function is working with all of that inside it, when it was originally declared with just "x." The only possibility I can think of is that this expression is treated as a single unit, but I'm not sure.
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Apr 4, 2013
Code:
if (IS_LEAP_YEAR(year))
const int days_per_month[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
else
const int days_per_month[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; Is it ok to declare the array in this manner or is it bad?
And i have to ask the user for a date to enter in my program. So should I use scanf or should I store the date in a string and then use sscanf. I have to check for valid input for everything like day, month, year etc. I did it as below..
Code:
int assignments;
assignments = scanf("%d / %d / %d", &month, &day, &year);
fflush(stdin);
if (assignments != 3)
{
printf("Retry: ");
}
else
error checking.
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Aug 1, 2013
Code:
#include <stdio.h>
int main(void){
int a=0;
for(;a<=10;)
int b;
return 0;
}
I have got a code like this. I don't expect to get an output but just assumed I would see the command screen until I terminated it. What I want to do is just declare a variable b in a endless loop. But what I got from the compiler is this error: error: expected expression before 'int'. I am using Code::Blocks and I think the compiler is GCC.
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