Error when allocating memory in c++

Question

I write a program using cpp to read strings with cin and save them in an allocated memory. An extra work I need to do is dealing with the circumstance when the size of the input is more than expected. When I testing the code, it doesn't display the content of the final memory saves, cannot terminate automatically. Here is the code.

#include <iostream>
#include <memory>
using namespace std;
int main(){
    allocator<string> sa;
    cout << "Please input the amount of words" << endl;
    int count;
    cin >> count;
    auto p = sa.allocate(count);
    cout << "Please input the text" << endl;
    string s;
    auto q = p;
    while(cin >> s){
        if (q == p + count) {
            auto p2 = sa.allocate(count * 2);
            auto q2 = uninitialized_copy_n(p, count, p2);
            while (q != p) {
                sa.destroy(--q);
            }
            sa.deallocate(p, count);
            p = p2;
            q = q2;
            count *= 2;
        }
        sa.construct(q++, s);
    }
    for (auto pr = p; pr != q; ++pr) {
        cout << *pr << " ";
    }
    cout << endl;
    while (q != p) {
        sa.destroy(--q);
    }
    sa.deallocate(p, count);
    return 0;
}

why using a allocator for this? I'm surprised that you use this instead of new or even better(!), a container like std::vector and std::string. — The Techel, May 06 '17 at 09:49

Marek R · Accepted Answer · 2017-05-06T10:05:58.367

5

Why do you use allocator? This template shouldn't be used directly in code. It suppose to be used to tweak behavior of STL containers. You are a newbie so do not touch it. This feature is for advanced developers to be used in extreme cases.

Simply just use std::vector<string> it has all features you need.

cout << "Please input the amount of words" << endl;
int count;
cin >> count;
auto v = vector<string> {};
v.reserve(count);

string s;
while (cin >> s)
{
    v.push_back(s);
}

edited May 06 '17 at 10:05

answered May 06 '17 at 09:51

Marek R

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Add a `reserve` call. – LogicStuff May 06 '17 at 09:56
Thanks for your suggestion. I attempt to do so because the book C++ primer incite me to do so. Indeed im a newbie : ) – code-life balance May 06 '17 at 10:08
apparently author of the book wants to proof how smart he is, instead writing a book which is teaches C++ starting from basics. Can you share a what book is it? – Marek R May 06 '17 at 10:16
@Saeron Is that "C++ primer" or "C++ primer plus"? The former is supposed to be good, the latter not so much (from what I've heard). – Angew is no longer proud of SO May 06 '17 at 10:30
@Angew Okay, since you are warm-hearted and persuade me, I will change the book you recommend. – code-life balance May 07 '17 at 16:29
1

@Saeron There's a list of [good C++ books](http://stackoverflow.com/q/388242/1782465) maintained by the community, you might want to take a look there. – Angew is no longer proud of SO May 07 '17 at 19:19

Error when allocating memory in c++

1 Answers1