C++ vector std::bad_alloc error in a program

Question

I was trying to sort a vector having user defined data type having two values, on the basis of one. But i get the error of bad_alloc. this is the code :

#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

struct s{
int value;
int weight;
};

bool comp(s a , s b){
return a.value>b.value;
}

int main(){
vector <s> p;
s temp;
int n;
cin>>n;
while(n>=1){
    cin>>temp.value;
    cin>>temp.weight;
    p.push_back(temp);
}
sort(p.begin(), p.end(), comp);
vector <s> :: iterator it;
for(it = p.begin(); it != p.end();it++){
    *it = temp;
    cout<<temp.value<<endl;
}

}

on running :

terminate called after throwing an instance of 'std::bad_alloc' what(): std::bad_alloc

can anyone help?

Answer 1

Problems that I see:

Infinite loop

In the loop

while ( n >= 1)
{
   ...
}

you are not changing the value of n. If n is greater 1 than at start of the loop, the loop will never end.

Not checking the status of input

You have

 cin >> temp.value;
 cin >> temp.weight;

You are not checking whether those calls succeeded. You are assuming that they did and proceeding to use temp.

Wrong way assignment

In the final loop, you are using

*it = temp;

That will change the vector, not extract the value from the vector.

---

Here's an updated version of main that should work.

int main()
{
   vector <s> p;
   s temp;
   int n;
   cin>>n;
   while(n>=1)
   {
      // If there is a problem reading, break.
      if ( !(cin>>temp.value) )
      {
         break;
      }

      // If there is a problem reading, break.
      if ( !(cin>>temp.weight) )
      {
         break;
      }

      p.push_back(temp);

      // Decrement n
      --n;
   }

   sort(p.begin(), p.end(), comp);
   vector <s> :: iterator it;
   for(it = p.begin(); it != p.end();it++)
   {
      // Extract the value from the vector and print it.
      temp = *it;
      cout<<temp.value<<endl;
   }
}