Delete part of dynamic array

Question

I created an array with the maximum dimension for text input. Now, I want to remove the remaining unnecessary part in order to free the memory. I am not allowed to use std::string, I need to use char[] arrays only.

Also, if you know better way how to use only char and allocate dynamic memory for text input, please help me. I do not know how many characters the user will enter

#include <iostream>

using namespace std;

int main()
{
    char *text = new char[256];
    cout << "Input text: ";
    cin.getline(text,256,'\n');
    while (cin.fail())
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max, '\n');
        cout << "Input text: ";
        cin.getline(text,256,'\n'); //need to delete part after '\n';
    }
    return 0;
}

You can't do that – you need to copy to another, smaller, array. It's not very clear what you think you need to delete or why, though. — molbdnilo
– molbdnilo, Commented Nov 27, 2017 at 12:59
@DenAndreychuk It is correct to tag this as C++, since that's what it is. However, you should have posted the artificial homework requirements as part of the question. Hang on, I'll edit it. — Lundin
– Lundin, Commented Nov 27, 2017 at 12:59

John Zwinck · Accepted Answer · 2017-11-27 12:50:43Z

5

Just use std::string instead of a C array of char. It will be sized automatically according to the input length.

Use the free function std::getline() instead of istream::getline():

string line;
getline(cin, line);

http://en.cppreference.com/w/cpp/string/basic_string/getline

answered Nov 27, 2017 at 12:50

John Zwinck

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3 Comments

Den Andreychuk Over a year ago

Ye, I know. But in my homework i must use only char. String type not allowed.

John Zwinck Over a year ago

If you write a question and tag it C++ you have to expect people with use C++ strings to answer it. You never said that wasn't allowed. I'm going to leave this answer here, as it addresses the question as written.

Den Andreychuk Over a year ago

Corrected. Sorry, this my first topic.

Raindrop7 · Accepted Answer · 2017-11-27 13:11:51Z

0

You can use a temporary dynamic array then copy the part you wanted from the original array then delete the original array then assign the original pointer to the temporary pointer:

char* szTxt = new char[256];
std::cin.getline(szTxt, 256, '\n');
std::cout << szTxt << std::endl;

const int size = strlen(szTxt);
char* szTmp = new char[size + 1];
strncpy(szTmp, szTxt, size);

szTmp[size] = '\0';

delete[] szTxt;
szTxt = szTmp;

std::cout << szTxt << std::endl;
std::cout << "Size: " << size << std::endl;

delete[] szTxt;

edited Nov 27, 2017 at 13:11

answered Nov 27, 2017 at 13:05

Raindrop7

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2 Comments

iBug Over a year ago

Your code will fail at szTmp[5] = '\0'. Increase the size by 1 at the new statement.

Raindrop7 Over a year ago

@iBug: Thanx! I didn't notice that. Edited.

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