long long v/s int in file input output in c++

Question

I tried many different unsuccessful ways, the last of which I am describing below-

#include<iostream>
#include<fstream>

//functions here


using namespace std;

int main(){
    int n;
    long long A[300001];
    ifstream myfile("sort.in");
    myfile>>n;
    
    for(int i=0;i<n;++i){
        myfile>>A[i];
    }
    cout<<A[0];
    myfile.close();
    
    return 0;
}

This doesn't work.

Whereas, the below one works-

#include<iostream>
#include<fstream>

//functions here


using namespace std;

int main(){
    int n;
    int A[300001];
    ifstream myfile("sort.in");
    myfile>>n;
    
    for(int i=0;i<n;++i){
        myfile>>A[i];
    }
    cout<<A[0];
    myfile.close();
    
    return 0;
}

What is the problem?

The only difference is use of int instead of long long. How does that make such a big difference? By the way, by not working I mean that it is not producing any output on the screen.

Are you running this from an IDE? If so, you need to figure out how to get your IDE to tell you what happened when you tried to run the program. — David Schwartz, Jun 25 '20 at 18:02
`long long A[300001];` remember the stack size is limited. On Visual Studio the default is 1MB on gcc the default can be around 10 times that. — drescherjm, Jun 25 '20 at 18:02

score 2 · Accepted Answer · answered Jun 25 '20 at 18:02

2

It's most likely a stack overflow problem caused by large statically defined arrays.

Instead of

long long A[300001];

use

std::vector<long long> A(300001);

answered Jun 25 '20 at 18:02

R Sahu

196,807
13
136
247

score 0 · Answer 2 · answered Jun 25 '20 at 18:06

0

in this case use of long long array may cause stack overflow.

try dynamicly alocated buffer:

#include<iostream>
#include<fstream>

//functions here


using namespace std;

int main(){
    int n;
    
    ifstream myfile("sort.in");
    myfile>>n;

    long long *A = new long long[n];

    for(int i=0;i<n;++i){
        myfile>>A[i];
    }
    cout<<A[0];
    myfile.close();

    delete []A;
    
    return 0;
}

answered Jun 25 '20 at 18:06

Ali Askari

445
3
7

Please don't use `new` in c++ (there are nearly always better techniques). In this case we should be using containers to store things like this (i.e. std::vector). – Martin York Jun 25 '20 at 18:10
Why do you ask not to use new? – levio_sa Jun 25 '20 at 18:16
1

@levio_sa millions of programmers have found, often to their detriment, that `new` is a lot harder to get right than it looks. As a result it's been mostly replaced (but not completely. Sometimes `new` is the only tool for the job) in modern C++ with safer options. See [Why should C++ programmers minimize use of 'new'?](https://stackoverflow.com/questions/6500313/why-should-c-programmers-minimize-use-of-new) for a longer discussion of the issues. – user4581301 Jun 25 '20 at 19:45

long long v/s int in file input output in c++

2 Answers2