I need to create a function in my program to open an input file and another function to open an output file and I need to use the files in other functions so Im trying to pass the stream object by reference but then i need a condition that tells the compiler not to reopen the file because then it will delete everything and make me input the file names again. Heres the two functions.
This actually should work, because it is passing address of polymorphisms object.I have tried changing prototype of test in Data.h, but failed.passing object address/pointers in C++.
I'm supposed to add two new functions to an existing class that I've written early on: readData(ifstream&)and writeData(ofstream&).
The parameters of the program are: -Create three employee objects as shown, -Create an ofstream object and open a file. Choose any name for the file that you want. Do not ask the user for the file name. Pass just the file name as the parameter (no path) so that your program assumes the file to be in the same folder as your executable file. -Send messages to each of the three Employee objects to write themselves out to the file. -Close the file. ...
If I get writeData(ofstream&) function bit to work! for brevity I've cut all the functions of the class that arent necessary. Here's what I have so far:
Employee.h #pragma once #include<string> using namespace std;
[Code] ....
So I've tried a bunch of different ways to get my objects into the ofstream object to write them to the file, but I'm supposed to use the two new functions somehow...but I'm way lost.
I am using the above code to retrive an item selected by user,But this line is giving an exception "Null Reference Exception, Object reference not set to an instance of an object"
Issue 1: I am using a stringstream object in a block of my program that needs to be visited repeatedly depending on a user's selection from a menu. I want the contents of this stringstream object to be cleared any time control gets to this part of the program. I have tried the clear and flush functions to no avail.
Issue 2: I am reading data from a source text file that would be regularly changed during the course of program run. After the program run is over, I am supposed to save the results(which is basically the source text file AND all updates) in a destination file. This destination file would then serve as the source file when next the program is run. In other words, I want a scenario where my results overwrite the original contents of the source file; implying that my source and destination files are now one, pretty much. How can I do this?
Try to implement overloading << operator. If I done it void then everything work fine (see comment out) if I make it class of ostream& then the operator return to me some memory address.
Code: #ifndef Point_HPP // anti multiply including gates #define Point_HPP #include <sstream> class Point { private:// declaration of private data members double x;// X coordinate double y;// Y coordinate
In Visual Studio 2010 C++ I have a series of existing text objects The text properties names are item1_lbl, item2_lbl, item3_lbl, ….
Based on a selection I want to change an object. I generate the name of the object I want to change in a string so from this string is there a way to get a pointer to the correct text object that is same name?
I have in my main(), a function that creates my arg object using boost/program_options.hpp i want to pass this object to another function using templates like this:
Code: template <typename Targ> void Count(Targ & arg){ MyObj<string> QueryTab(arg["input-file"].as<string>()); //line number is 352 ... }
However I get an error:
Code: ../include/Filter.hpp: In member function ‘void Count(Targ&)’: ../include/Filter.hpp:352:40: error: expected primary-expression before ‘>’ token ../include/Filter.hpp:352:42: error: expected primary-expression before ‘)’ token ... obviously it does not recognize my intention, what did I do wrong?
I make a class (it stands for an ARMA time series), and I have a method wich modifies some of its variables. In other part of my program I have a function wich receives one object of this class as a parameter and, at some point, it calls the method of the ARMA class to modify it; here is my deal I want to pass the ARMA class by reference to this function, because I want the variables of the instance I'm passing to be modified, not those of a copy the method uses. Also, I would like not to declare the function inside the class ARMA, cause I use it in other places too (it's basically a Nelder-Mead optimization what it performs).
Here is a code wich sketches what I've been trying, and exactly the error message I get is "modifyParameter has not been declared".
#include <iostream> #include <cstdlib> using namespace std; class ARMA{
I suspect the syntax of the declaration, but I am not sure what to do here? If I change the call to the function, then the array ( matrix ) is passed by value, and it takes forever:
Code: int read_files(std::string fname, int nCols, int nRows, ss_matrix_t ssMat ) // this takes ages ( it does compile and link )
I'm having trouble using a stack's functions when passing it by reference.
I'm currently messing around with passing a pointer to the stack instead, but to no avail.
The problem is in my placeInto function. I will label, in my code, where the program stops.
The program is an RPN Calculator, designed to receive keyboard input of an infix mathematical string, convert the infix string into a postfix mathematical string, and then solve the string. The program then outputs the postfix string and the solution.
The program loops through until closed via force-close, as was assigned.
*/ #include <iostream> #include <string> #include <stack> using namespace std; /////////////////////// // function prototypes // /////////////////////// // u = unfinished /* 1*/void welcome(); // welcome screen
Every time we pass an object to a function, and when the function ends and the object is not necessary anymore the destructor is called. if it's passing by value then a copy of the object is passed. if the object has a pointer inside of it so we implement the copy constructor to create a new pointed-variable so the original pointer will not get deleted.
so far so good. But what about passing an object to a non-member function by reference?
The language says that as soon as the function ends - the object will be deleted , because we passed by ref. that means that after the function ends - the object is not usable anymore! =What does that say? that in c++ you can't pass object by ref. because it will get deleted and un-uasable??
Varifying it with a compiler shows that the object is NOT deleted after the function ends.
I created the following code to pass the the variable 'inputVoltage' by reference to the function 'input'. It certainly works when I run the program, but I dont think it is a standard way of doing it, i.e. the use of '*' and '&' is not according to convention ? Or perhaps the way did it is acceptable ?
int input (double *inputVoltage); int main ( { double inputVoltage; input(&inputVoltage);
Suppose I have a stl vector of ints, and I want to pass a sub-range of that vector as an argument to a function. One way of doing that would be to copy the sub-range, and then pass that copy by reference, as follows:
Code: #include <vector> using namespace std; int MyFunction(vector<int> &a_vector) { // Do something return 0;
[Code] ....
However, it can be time-consuming to copy the elements between the two vectors if my_vector is large. So I'm wondering if it is possible to directly pass a sub-range of my_vector by reference, without having to create a new vector and manually copy over all of the relevant elements?
All entities need to be stored in the dynamic memory. I managed to force this by making the constructor private and by adding a static method which dynamically creates an object and returns a pointer. But it is most likely that the user will want to make them dynamically and we still have the following problem.
entity* player = entity::create(); (*player).setPosition(something); (*player).act(); (*player).draw();
You get the point, having to dereference the pointer before each call becomes painful. So I thought about this... Instead of returning a pointer, I can return a reference. Then the code is much cleaner.
{ entity& test = entity::create();
// do stuff... test.act(); // more stuff...
test.destroy(); // deletes the dynamic object }
I put this code between brackets. That's because we must make sure the reference test doesn't exist after destroy is called, because destroy() makes it invalid. This is fully functional and won't cause any problem as long as the user doesn't forget to never call any method on a destroyed entity. But it's evil code. Would you risk it, or is there another way around?
When returning an object by reference, only the address of the returned-object is returned, and that way we spare pushing a large object into the stack, and also spare time of pushing and popping large object to/from stack.
But what happens when the object that receiving the returned-object, is not a reference, but a 'regular' object?
How is the content of the returned object copied into the receiving object?
See for example in main, wid vs rwid. (I know in the case the returned-object is just one variable, there's no need to return it by reference, but its for simplifying the code).
class Rectangle { public: Rectangle(int w=0, int h=0);
I have this method that takes a pointer to a class object and right now when printing it, it's returning the location in memory 0x100300000. I've tried tweaking the function in a few different ways but I cant get it to return the object instead of the location.
Here's the vector that addSale accesses and the deceleration of the addSale ethod in the employee class.
I have a program that is working very well when I pass C++ vectors as arguments to my functions by reference, but I get some compilation errors when try to make a modification. I am also posting the entire program and its output below. so that you can see what is going on. I have commented out the line that causes an error.(Some of the indentation that got corrupted when I copied the code to the browser.)
This program basically calculates the coefficients of a least square polynomial and then evaluates this polynomial at artificial data points and verifies that this actually reproduces the original data within reasonable floating point error.
The function that computes the coefficients of the least square polynomial is Code: vector<double> LSPVecValued_GSL( const int, const vector<float> &, const vector<float> &); and as you can see it returns a vector by value, and this vector contains the coefficients of the least square polynomial.
There is also a function that evaluates this polynomial by accepting a vector argument by reference : Code: float evaluate_polynomial(double, vector<double>& ) ; I have also created another version of the evaluation function which accepts the same vector argument by value: Code: float evaluate_polynomial_ByValue(double t, vector<double> vec_a) ; In the program I call the first evaluation function (whose vector argument is passed by reference) by first using an intermediate vector variable containing the coefficients, and then I pass this vector as an argument to the evaluation function, as follows:
Code: vec_a = LSPVecValued_GSL( deg, vec_x , vec_y); for(int j=0; j< n ; j=j+20 ) { cout<<"x["<<j<<"] = " << vec_x[j] << " ,y["<<j<<"] = " << vec_y[j] <<" , p(x["<<j<<"]) ( EVALUATED FROM REFERENCE) = " << evaluate_polynomial( vec_x[j], vec_a) << endl; // This version works without error
[Code] .....
As you can see above, I am also able to call the second evaluation function (the one whose vector argument is passed by value) directly by plugging in the function LSPVecValued_GSL"(...)" and this works without error, and this is a one step process, only one line of code is involved.
However, I get a compilation error (line number 12 that I have commented out above) if I try to plug in the function "LSPVecValued_GSL(...)" into the first evaluation function that expects a vector argument by reference. I tried to put a "&" in front ofLSPVecValued_GSL but this did not fix the bug.
What syntax is appropriate to use the first evaluation function (which accepts a vector argument by reference) if I want to plug in the vector-valued function LeastSquarePolynomial_GSL directly in the the first version of the evaluation function which expects a vector argument by reference?
I am working on incorporating a function in to an already existing piece of code, I have incorporated the function fine as far as I am aware.
The problem I have is that I am trying to pass two int arrays to the function, so that i can manipulate and compare them "the values will be changed the originals cannot be changed"
I am having trouble pulling the information out of the already created array, I am able to pass the pointer reference for the single value which is not exactly what i want "best_prog".
My function is below I have commented the memcpy parts and also the majority of the code isn't there cause it is not needed to see make the copy work.
int edit_distance(int index) { struct prog *progp = &population[best_prog]; /* The struct of best prog not sure if i need one for the other prog I am trying to compare it with the one below doesn't work as intended.*/ //struct prog *progp = &population[]; int editdistance = 0, ar1 = 0, ar2 = 0, a = 0, b = 0, j = 0, x = 0;
