Memory Limit Exceeded while reading integers into the vector - c++

Question

I am trying to read integer values from text file into a vector.
Input file ip1.txt has the following content:
4
-1000 -2000 -3000 -4000
int maxsub(vector<int> a, int size)
{
a.erase(a.begin());
vector<int> sum;
for(vector<int>::iterator w=a.begin(); w <= a.begin()+size-1; ++w)
{
int j;
int s=*w;
for(int t=0; t <= size-1; t++)
{
j = s + a[t];
sum.push_back(j);
}
a.pop_back();
}
std::sort(sum.begin(),sum.end());
int u = sum.size()-1;
int m = sum.at(u);
return m;
}
int main()
{
std::vector<int> nums( (std::istream_iterator<int>(std::cin)),
std::istream_iterator<int>() );
int k = nums[0];
int u = maxsub(nums,k);
cout << u <<endl;
}
I am getting Warning message as 'Memory Limit Exceeded'
How can i resrict vector to read only till -4000 in the input file,I am using file redirection
*./123 < ip1.txt *

Answer 1

Bug at the source code.
All loops in maxsub()
for(vector<int>::iterator w=a.begin(); w <= a.begin()+size-1; ++w)
for(int t=0; t <= size-1; t++)
has iterations from 0 to size-1 elements (=size all in all elements), but after code
a.erase(a.begin());
vector 'a' has only (size-1) elements.
Therefore, all for-operators is 'outside-the-boundary'.
I think, it's cause of warning message.

Answer 2

If you know that the first number will be the length of your vector, why not take advantage of it?:
int length = 0;
std::cin >> length;
std::vector<int> numbers;
numbers.reserve(length);
then you can just use simple for loop that checks whether the number has been successfully extracted from the stream and also prevents more than specific amount of numbers being read:
int number;
for (int i = 0; (i < length) && (std::cin >> number); ++i)
{
numbers.push_back(number);
}
Don't forget to #include <iostream>, #include <sstream> and #include <vector>. Also note that std::cin can be easily replaced with file stream :)

Answer 3

Write a for loop
std::vector<int> nums;
int size;
std::cin >> size;
for (int i = 0; i < size; ++i)
{
int val;
std::cin >> val;
nums.push_back(val);
}

Answer 4

'a.begin()+size-1' is before begin():
Having
for(vector<int>::iterator w=a.begin(); w <= a.begin()+size-1; ++w)
and
int k = nums[0];
int u = maxsub(nums,k);
and
nums[0] = -1000;
size is -1000
If you want to exclude the first and last element:
if( ! a.empty()) {
// Not erasing the first element: a.erase(a.begin());
for(vector<int>::size_type i = 1; i < a.size() - 1; ++i);
}