C++ :: Passing Sub-range Of A Vector By Reference
Dec 18, 2012
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?
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Nov 30, 2014
I asked a few questions a few weeks ago about vectors and the fact that their data is stored on the heap. When a function closes, anything in its scope is destroyed, if it's passed by reference it won't be destroyed since it's outside the scope.
I have a program where I create a vector in one function, then pass it by reference to another. When I test for memory leaks, I get told I have 1 memory leak in in my start() function, and one memory leak in my save() function.
It's just a simple program that creates a vector, populates it with some numbers, then saves the numbers in a file. If I'm passing my vector by reference to another function, do I need to manually do something to avoid memory leaks? I'll post the code below.
#include <vector>
#include <iostream>
#include <iomanip>
#include <cmath>
[Code].....
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Aug 18, 2014
I keep getting this "Debug Assertion Failed" error that says:
expression: vector subscript out of range
I tried to make the loop the same as the vector size, but I'm still getting the same errors.
void Grid::output(ostream & out) {
vector<vector<int>> grid(4);
int rows, columns;
out << " 0 1 2 3 " << endl;
out << " +---------+" << endl;
for( rows=0; rows<grid.size(); ++rows ) // make each row
[code]....
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Jul 31, 2013
I'm making a simple game and I'm having trouble creating boundaries for the players movements. The map is a 2D vector. When I compare the vector with the players current position sometimes I get an error during run. When the error isn't occurring the behavior of the boundaries is bizarre. The error tells me that the vector is out of range.
Here is the where the map is created. It's within its own class constructor.
vector< vector<char> > map_parts;
map_parts.resize(25);
for ( int i = 0; i < 25; i++ )
{
[Code].....
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Jul 18, 2014
I'm trying to do some operator overloading, the function is supposed to add the values at index [i] of two vectors and place the result in the returning vector. The problem is I keep getting a vector out of range. This is the overloaded operator I'm working with (relatively new to these):
vector<float> operator+(const vector<float>& a, const vector<float>& b){
unsigned long size;
vector<float> temp;
if(a.size() >= b.size())
size = a.size();
[Code] .....
and then I would do something like this in the main:
vector<float> v, v1, v2;
v1.push_back(9.1);
...
v2.push_back(8);
...
v = v1 + v2;
but when I try to output the vector v I just get a vector out of range exception.
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Feb 13, 2013
When i build this program i get no errors, however a message appears saying vector subscript out of range. What does this mean and what can i do to mkae my program work
#include <iostream>
#include <ctime>
#include <cstdlib>
#include <iomanip>
#include <cstring>
#include <time.h>
#include <vector>
using namespace std;
[Code] .....
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Dec 19, 2013
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?
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Aug 26, 2014
Why wouldn't this code compile when adding '<double>' after the function call?
template<class T>
T add(T& a, T& b){
return a + b;
}
int main() {
int a, b;
cin >> a >> b;
cout << add<double>(a,b);
}
Compiler error:
cannot convert 'a' (type 'int') to type 'double&'
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Mar 1, 2013
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{
[code]....
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Dec 31, 2012
How can I pass a matrix as a reference parameter? I am using the following declarations:
Code:
typedef std::vector< std::vector<std::string> > ss_matrix_t;
I declare the matrix with the following statement, where nRows and nCols are integers
Code:
std::vector< std::vector<std::string> > vI2Matrix(nRows, std::vector<std::string>(nCols,""));
The function is called with:
Code:
int read_files(std::string fname, int nCols, int nRows, ss_matrix_t &ssMat )
But I get a linker error:
error LNK2019: unresolved external symbol "int __cdecl read_splayed_files(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int,int,class std::vector<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::allocator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > >,class std::vector<class std::vector<class
[Code] ....
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 )
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Feb 21, 2012
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
[code]....
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Oct 17, 2014
I will try my best to describe this problem I am having because I am not sure if I can reproduce the error in a small code example as this is part of a large code project.
I have a plain std::vector which contains pointers to objects.
When attempting to delete the objects, even if I know for a fact that the std::vector has at least one object in it as shown by the debugger, I get the "Vector Subscript Out of Range" error.
I'll even do a range for loop like so:
for (auto & e : CurrentObjects) {
delete e;
}
And yet I still get the "Vector Subscript Out of Range" error. The destructor is never called for the object represented by "e" so I am not sure why I get the error.
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Jun 5, 2014
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.
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Aug 28, 2014
Why it is necessary to use the reference operator here ?
const string& content() const {return data;}
Example in [URL] ....
// classes and default constructors
#include <iostream>
#include <string>
using namespace std;
class Example3 {
string data;
[Code] .....
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Mar 4, 2013
If f1 and f2 are two user defined functions.
main(){
int *p;
f1(&p)
}
f1(**p){
f2(&p);//
If I've to pass the pointer by reference again in another function, will I've to do something like this?
}
f2(***p){
**p = NULL;
}
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May 5, 2014
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.
void InputFileOpen(ifstream &inFile) {
string file_name;
if(!inFile.is_open()){
cout<< "Enter the input file name: ";
cin>> file_name;
inFile.open(file_name, ios::in);
[code]....
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Sep 10, 2014
I define an integer variable and pass it by reference to a function.
int func(int &x)
{
// do something
}
int x;
func(x);
However, I have not only one variable but an array of variables with its predefined name. How do I pass to the function by using loop? Example:
int x, y, z;
func(x);
func(y);
func(z);
How can I do this by using loop?
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Nov 23, 2013
Code:
#include <Data.h>
int main(int arg_count, char** argv) {
if(arg_count!=3){
cerr<<"Files misisng
";
exit(1);
[code]...
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++.
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Sep 25, 2012
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);
[Code]....
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May 23, 2014
I'm implementing an normal_distribution to select objects on a vector. The thing is I can't use values greater then 1 or less then -1. Here is what could be done:
gausx=gaus_distributionx(generator);
while((gausx>1) || (gausx<-1))
gausx=gaus_distributionx(generator);
The question is if the distribution would loose it's power to be a normal distribution, because some of the gerated numbers wouldn't be used. Any way to set ranges for the distribution?
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Sep 3, 2014
You are to write a C++ program to generate random integers in the range [ LOW = 1, HIGH = 10000 ] and to store them in a vector < int > of size VEC_SIZE = 250. Then, sort the contents of the vector (in ascending order) and display it on stdout.
To sort the contents of a vector, use the sort ( ) function from the STL. In addition to the main ( ) routine, implement the following subroutines in your program:
• void genRndNums ( vector < int >& v ) : This routine generates VEC_SIZE integers and puts them in vector v. Initializes the random number generator (RNG) by calling the function srand ( ) with the seed value SEED = 1, and generates random integers by calling the function rand ( ).
• void printVec ( const vector < int >& v ) : This routine displays the contents of vector v on stdout, printing exactly NO_ITEMS = 12 numbers on a single line, except perhaps the last line. The sorted numbers need to be properly aligned on the output. For each printed number, allocate ITEM_W = 5 spaces on stdout.
Programming Notes:
• You are not allowed to use any I/O functions from the C library, such as scanf or printf. Instead, use the I/O functions from the C++ library, such as cin or cout.
• Let v be a vector of integers, then the call: sort ( v.begin ( ), v.end ( ) ) sorts the elements of v in ascending order. The detailed description of the sort ( ) routine can be found on the course web site and in the course textbook.
• Execute the srand ( ) function only once before generating the first random integer with the given seed value SEED. The rand ( ) function generates a random integer in the range [ 0, RAND_MAX ], where the constant value RAND_MAX is the largest random integer returned by the rand ( ) function and its value is system dependent. To normalize the return value to a value in the range [ LOW, HIGH ], execute: rand ( ) % ( HIGH – LOW + 1 ) + LOW.
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Apr 21, 2014
I have the following code. however, when I debug it gives an error saying" vector subscript out of range"
Vector based mufti-dimensional arrays
Vectors are a STL container that allow you to store pretty much anything in them. When used correctly they can be very powerful containers.
They provide an added benefit that they will automatically remove the memory they use when they go out of scope. This means that objects stored within a vector do not need to be de-allocated (but pointers to objects do). You can also do some interesting things with dynamic multidimensional arrays with vectors.
For example, if you only allocate the first dimension, then use the .push_back() to add records to the 2nd dimension it's no longer a grid, but an array with a dynamically sized 2nd dimension (much like a street of buildings each with a different amount of floors).
This functionality can be achieved using pointers, but is much harder to do.
#include <iostream>
#include <vector>
#include<conio.h>
using std::vector;
using namespace std;
[code]...
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Mar 12, 2014
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?
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Mar 16, 2013
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;
[code].....
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Jan 24, 2015
Does putting a ref when passing a struct to a parameter work? Say i have this code
struct struct1 {
public int i;
public void show() {
Console.WriteLine(i);
[Code] ....
The output doesn't change. The result is
0
100
500
0
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Nov 3, 2013
My project's goal is to read some numbers from input file,then create a grid.my input file is:
2 3
3 4 5
1 2 4
first line is rows and colums. second and third line the grid location values.My code is
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
#include<vector>
using namespace std;
[code].....
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