C++ :: Find Function - Return Reference To A Vector
Oct 12, 2014
Okay, so for an assignment I need to write a function called find() that returns a reference to a vector. So I have vector <int> & find(string & key); If I do this, I get the obvious warning warning: reference to local variable 'lineNum' returned [enabled by default].
If I do vector<int> & find(string & key) const; I get a huge error that starts out like
In member function 'std::vector<int>& index_table::find(std::string&) const':
indextable.cpp:74:30: error: no match for 'operator='
The place where I should put the return value is marked with ???. SEntityPhysicalizeParams is a struct from another header from which I dont have access to it's source file.
I tried several things but noone seemed to work out and keep getting me either error "function must return a value" or "initial value of reference to non-const must be an lValue".
Here is SEntityPhysicalize where my function is refering to:
I have asked a related question before, and it was resolved successfully. In the past, when I wanted to use std::max_element in order to find the maximum element (or even sort by using std::sort) of a vector of structures according to one of the members of the structure, all I had to do was to insert a specially designed comparison function as the third argument of the function std::max::element. But the latter comparison function naturally accepts two arguments internally.
For instance, here is a test program that successfully finds the maximum according to just one member of the structure:
And the output was this, as expected: Maximum element S.a of vector<S> vec is at: 9 [I]max element of vec.a between slot 3 and slot 6 is: 6, and its index is: 6 vec[6].a = 6 [I]max element of vec.a between slot 4 and slot 7 is: 7, and its index is: 7 vec[7].a = 7 [I]max element of vec.a between slot 5 and slot 8 is: 8, and its index is: 8 vec[8].a = 8 [I]max element of vec.a between slot 6 and slot 9 is: 9, and its index is: 9 vec[9].a = 9
However, I now need to search and find an element of vector<myStruct> according to just one member of myStruct, instead of finding the maximum or sorting as before. This presents a problem because the function std::find does not accept such a comparison function as its third argument.
This was the description of the std::find function that I found: find - C++ Reference
Code: template <class InputIterator, class T> InputIterator find (InputIterator first, InputIterator last, const T& val);
I could also find another function called std::find_if, but this only accepts a unary predicate like this: find_if - C++ Reference
Code: template <class InputIterator, class UnaryPredicate> InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred);
And once again this is either inadequate of I don't see how to use it directly, because for the third argument I would like to insert a function that takes two arguments with a syntax like this:
Code: int x=7; std::vector<S>::iterator result; result = std::find(vec.begin(), vec.end(), []( const (int x, const S & S_1) { return ( x == S_1.a ) ; } ) ;
Is there another std function that I can use to make search and find an element according to just one member of myStruct?
Or perhaps there is a clever way to pass two arguments to the unary predicate.
std::vector<double> calculate_mag_response(double start_freq, double end_freq, int N, std::vector<double> num, std::vector<double> den
The function should return a vector size N of magnitude responses in decibels of the transfer function defined by numerator and denominator vectors num and den. To adequately test, you should drive this with more transfer functions.
#include <vector> #include <iostream> #include <cstdlib> #include <ifstream> using namespace std; int main(int argc,char *argv[]) { vector<double> myNum, myDen, results;
How to pass my array to the function and return it as a sorted vector. I'm kind of lost with the functions part.
Problem: Write a program that performs a sorting routine as discussed in class. Create an array of 10 integers (e.g., 63, 42, 27, 111, 55, 14, 66, 9, 75, 87). Pass this array to a separate function that sorts the integers and returns a vector containing the sorted integers. Use either the SELECTIONSORT algorithm or the INSERTIONSORT.
#include <iostream> using namespace std; int n; int& test();
[Code] ....
Explanation
In program above, the return type of function test() is int&. Hence this function returns by reference. The return statement is return n; but unlike return by value. This statement doesn't return value of n, instead it returns variable n itself.
Then the variable n is assigned to the left side of code test() = 5; and value of n is displayed.
I don't quite understand the bold sentence. Shouldn't value of n and variable n be the same?
I defined the following function to find out the iterator of a certain value in the vector. I defined it as such so if the value exist in the vector then return a iterator of it, if not then return a pointer pointing to nonsense.:
I have a cpp app that reads in a number of files and writes revised output. The app doesn't seem to be able to open a file with a ' in the file name, such as,
N,N'-dimethylethylenediamine.mol
This is the function that opens the file :
Code: // opens mol file, reads in rows to string vector and returns vector vector<string> get_mol_file(string& filePath) { vector<string> mol_file; string new_mol_line; // create an input stream and open the mol file ifstream read_mol_input; read_mol_input.open( filePath.c_str() );
[Code] ....
The path to the file is passed as a cpp string and the c version is used to open the file. Do I need to handle this as a special case? It is possible that there could be " as well, parenthesis, etc.
I have code here that uses assignment operators that doesn't return by reference and it still works. So why does my book say you need to return by reference?
Here is a quote from my book:
The return type of operator= is a reference to the invoking object, so as to allow chained assignments a=b=c.
The code below is from my book. I simply removed '&', in the original code that has assignment operators return by reference, from IntCell & operator=. This way the assignment operator no longer returns a reference, and it still works.
#include <iostream> using namespace std; class IntCell { public: explicit IntCell( int initialValue = 0 ) { storedValue = new int{ initialValue }; }
I'm writing some functions pertaining to binary trees. I've used recursion once before while learning quicksort but am still quite new and unfamiliar with it. And this is my first time touching a binary tree. So my question: In my addnode function, will the return root statement at the end ever return a value other than the value passed to the function?
Code: #include <iostream> #include <vector> using namespace std;
class A{
[Code]....
I read somewhere, that we can imagine the reference as a pointer to the vector. So, my question is:
Let's assume that instance of class A, named a, was created with new. We call a.getV() to foo and then we call the destructor of a. foo is safe? Is the copy constructor of std::vector called?
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?
im using a for loop to find the index values of the tied high scores and store them into string list then reference list in the second for loop to output it to screen however it isnt letting me use an array with index i as an index its self.
void printHighest(Student s[], int length){ int index; string list[10];//you're never going to have more than 10 people with a tieing highscore. index = findMax(s, length);
[Code] ....
For the time being I simply removed the idea of string list and just put the contents of the second for loop into the if statement above it. However, I am still curious as to if I can reference an index of an array in an index of another array.
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.
I passed the address of the vector to the function. And then display the address. It is a pretty common operation. But it just won't work. But then we do something simple similar to that of the vector. But it works.
Here is my code to find the index of a string array whose string is equal to the query string. I have checked the program can return the correct index, but the cout result is totally wrong.
#include <iostream> #include <string> using namespace std;
The error is unclear but suggests Its received a bad pointer from another heap. It references dbgheap.c line 1322 and assertion failure
I have two string vector functions the first is called from the main function, the second is called from the first.
Their purpose is to receive a string of text and numbers in a semi-specific format, which the main body of the code reads from a text file, and delaminates the data as to return the first variable in the string as the variable name and the second as the variable value. Along the way it filters out a lot of the unwanted whitespace and punctuation.
E.g "{ VariableNameA 123 }" would be returned as "VariableNameA" And "123"
The code works perfectly for most of the lines in the text file but fails on one particular line where the first variable is 25 characters long. Basically it works for anything 22 characters or less. There are never more than 4 elements in the vector and each element is never intended to be longer than 25 characters.
It fails trying to return from the second split function to the first split function.
Is there a limit to the size of each vector element? I'm struggling to find a way round this without having to rewrite the whole thing.
How to output vector contents using the push_back function. My program reads in values just fine, but it does not output anything and I've been stuck on why.
here is my code:
#include <iostream> #include <array> #include <vector> using namespace std; int duplicate( vector < int > &vector1, const int value, const int counter)
So the program reads contents from a text file into a vector and then the user enters in a string that they want to search for. The program iterates through the vector to find the string and then saves that line to another vector to display later(incase there is more then 1 instance of the string found).
Here is what I have atm:
void doSearch(vector<string> &phonelist, string searcher, vector<string> &holdNumbers) { int i = 0; string value;
[Code].....
I just get an R6010 error -abort() has been called.
Ok my assignment has me doing vector math with some canned code provided for me by the instructor This is the header file to the class I'm working with and the .cpp file as far as I've gotten it.
#pragma once #include "Scalar.h" class Vector2D { public:
Vector2D(); Vector2D( const Vector2D& ) ;// copy constructor Vector2D( Scalar element[2] ) ; // initialize with an array
[Code] ....
I'm having trouble seeing which data members I'm multiplying together and what the initial state, continuing state, and after loop action I'm supposed to be using in the for loop.
