CODEWITHSUNDEEP
c++
user18348324
user18348324

Reputation: 262

How can I correctly keep track of stream position?

I am writing a program which requires me to take in double inputs from the user in a very specific way, so I'm learning about streams.

In the end, my goal is to force the user to format their input in the way I desire, which is:

2.0 3.0 4.0 -> doubles (or integers) with spaces in between and no trailing spaces

I've been using a std::istringstream to read inputs in a way akin to the following example:

#include <iostream>
#include <sstream>
using namespace std;

int main(){
    int a[5] = {0};
    
    while (1){
        cout << "Input: ";
        string s;
        getline(cin, s);
        istringstream buffer(s);
        
        for (int i = 0 ; i < 5 ; i++)
            buffer >> a[i];
        
        for (int i = 0 ; i < 5 ; i++)
            cout << a[i] << " ";
        cout << endl;
    }
}

My question is about the following terminal input/output:

Input: 1 2 3 4 5
1 2 3 4 5 
Input: a b c d e
0 2 3 4 5

Why is the output for the characters being put into integers the way it is?

Here is another example:

Input: 5 6 7 8 9
5 6 7 8 9 
Input: a b c d e
0 6 7 8 9

It seems to be defaulting to 0 for the first encountered character, and then reusing the rest of the stream, which is why I'm asking about stream position.

My expectations:

  1. Either it would be the corresponding ASCII numerals.

  2. They would all be 0, since (for a reason that I would like to know), characters inputted from a stream into an integer tend to default to 0.

I believe the output being the way it is has to do with the stream position, and I would like it explained (along with an answer on the defaulting 0 characters).

Basically, I'm curious about streams and would like to know more about how they're handled, and this seems like a quirk that could highlight that.

Upvotes: 0

Views: 147

Answers (1)

john
john

Reputation: 87957

Here's the full explanation for your output.

I'm concentrating on the input of a.

The first step is that the read fails because a is not a valid integer. This puts the cin stream into an error state and sets a[i] to zero.

The next step is that cin >> a[i]; returns and the program prints the value from step one.

Now the stream is in an error state (from step one) all subsequent reads fail immediately, with no change to any a[i], so the previous values are printed.

So nothing to do with stream position.

Upvotes: 2

Related Questions