Thread: Delete object created in the function

Hi ,

I'm a beginner at C++ and I've created a code in order to reverse statement and gets vowels from it. it's an exercise.
In the getVowels function I've allocated an array in order to fill it with found vowels and return the stream to main().
I know that dynamic memory is resident on Heap therefore it isn't a local storage.
How do I free the memory ?Where I have to insert delete[] ?

Code:

#include "pch.h"
#include <iostream>
#include <string>

using namespace std;

string reverse(string str);
string getVowels(string str);

int main()
{

    string statement = "The best is yet to come";

    string reversed;
    string vowels;
    
    std::cout << "Hello World!\n";
    cout << "Statement: " << statement << endl;

    reversed = reverse(statement);
    cout << "Reversed: " << reversed << endl;
    
    vowels = getVowels(reversed);
    cout << "Vowels: " << vowels << endl;

        
    return 0;
}
string getVowels(string statement) {
    
    char vowels[] = { 'a','e','i','o','u' };
    int len = statement.size();
    int cont = 0;

    char *foundVowels = NULL;      
    foundVowels = new char[len]; // Allocated space like statement lengh

    cout << "\nSize: " << len << endl;
       
    for (char c : statement) {

        for (char vowelsList : vowels) {

            if (vowelsList == c) {
                foundVowels[cont++] = c;
                // cout << vocale << " " << carattere << " " << cont << endl; // debug
            }
        }
    
    }

    foundVowels[cont] = '\0'; // clean string
     
    return foundVowels;

}
string reverse(string statement)
{
    int len = statement.size();
    string invertiStr = statement;

    cout << "\nSize: " << len << endl;

    for (char c : statement)
    {
        invertiStr[--len] = c;
        //cout << c << " " << len << endl; //debug
    }
    return invertiStr;
}

The solution has been to add a new string in the local function and
copy on it the result from foundvowvels[] :

Code:

string result;

...............................
result = foundVowels[cont];

delete[] foundVowels;

return result;

might I ask to you if that is a good practice or I've got a bad idea ?

Thanks

Well making a string result is the way to go in your code at the moment.

> foundVowels = new char[len];
But your code is broken if the input is all vowels.
You're one short on the amount of space you need.

Since you could also do
string result;

then later append characters to your result
result += c;

The whole messy manual memory management (and the risk of getting it wrong) goes away.

You should be aware that in terms of naming, this doesn't make sense:

Code:

for (char vowelsList : vowels) {

vowels forms the range that you're iterating over, which means that vowelsList is a vowel, not a list of vowels, so you should have named it vowel.

Instead of directly looping over the vowels, I would have stored them in a string that could be searched:

Code:

string getVowels(const string& statement) {
    const string vowels = "aeiou";

    string result;
    for (char c : statement) {
        if (vowels.find(c) != string::npos) {
            result += c;
        }
    }
    return result;
}

Notice that I have made statement a const reference since you don't need a copy of the statement from the caller, and you don't need move semantics.

If you were feeling more adventurous, you could #include <algorithm> and replace even that remaining loop:

Code:

copy_if(statement.begin(), statement.end(), back_inserter(result),
        [&vowels](char c) { return vowels.find(c) != string::npos; });

EDIT:
There is yet another way, but it is fundamentally different from your approach, but perhaps it is good to keep in mind. What you did, and what I showed you, are variations on the theme of "copy vowels from the source to the result". This other way is "remove non-vowels from a copy of the source to become the result":

Code:

string getVowels(string statement) {
    const string vowels = "aeiou";

    statement.erase(
        remove_if(statement.begin(), statement.end(),
                  [&vowels](char c) { return vowels.find(c) == string::npos; }),
        statement.end()
    );
    return statement;
}

You would see that I have changed the function parameter back to string so that a copy is made, and then use the remove_if algorithm to "remove" the characters of statement in-place such that all the non-vowels are at the end. Then, I call statement's erase member function to erase the "removed" characters, leaving the vowels that are then returned.

I 've understood and I'm going to update the code.

string.find() is great it makes c++ look a very high level language

I've found "remove_if" syntax , but i don't know what "erase" means or where I can read about it.
May be it's an advanced topic and I should postpone it.

Thanks

string - C++ Reference

Originally Posted by Nwb

How were you able to color your code in that way?

I'm sorry. I didn't notice much.
I retry:

Go Advanced
Use CODE TAG
copy paste from Visual Studio

Code:

       string statement = "The best is yet to come";

    string reversed;
    string vowels;


    std::cout << "Hello World!\n";
    cout << "Statement: " << statement << endl;


    reversed = reverse(statement);
    cout << "Reversed: " << reversed << endl;


    vowels = getVowels(reversed);
    cout << "Vowels: " << vowels << endl;

Edit:
no color

> How were you able to color your code in that way?
You shouldn't.

99% of the time, when people copy/paste marked-up code (ie, includes font/colour tags), the result on the forum is a horrible mess.

Just copy-as-text / paste-as-text and the board will do just fine.

To see the color after pasting as text; I often have to refresh the page.

Tim S.

Originally Posted by Nwb

Can you copy from Visual Studio with the color though? I thought you could only copy text. How might OP have done that? Weird..?

Tim I'm referring to OP's original topic post, do you notice that the text itself is colored?

To see how that did the stupid thing do reply with quote.

Tim S.