CODEWITHSUNDEEP
c++fstream
otisonoza
otisonoza

Reputation: 1344

Cannot read big int from ifstream

I have a txt file:

4286484840 4286419048 4286352998

(They are RGB values.)

I would like to store them in a vector.

void read_input(const char* file, std::vector<int>& input)
{
    std::ifstream f(file);
    if (!f)
    {
        std::cerr << file << "Read error" << std::endl;
        exit(1);
    }

    int c;
    while (f >> c)
    {
        std::cout << c << std::endl;
        input.push_back(c);
    }

    std::cout << "Vector size is: " << input.size() << std::endl;
}

The result is:

Vector size is: 0

However with the following file:

1 2 3

The result is:

1
2
3
Vector size is: 3

What is wrong with the first file? Are the numbers too big?

Upvotes: 1

Views: 913

Answers (2)

user3028983
user3028983

Reputation: 1

void read_input(const char* file, std::vector<unsigned long int>& input)
{

    std::ifstream f(file);
    if (!f)
    {
        std::cerr << file << "Read error" << std::endl;
        exit(1);
    }

    int c;
    while (f >> c)
    {
        std::cout << c << std::endl;
        input.push_back(c);
    }

    std::cout << "Vector size is: " << input.size() << std::endl;
}

Upvotes: 0

Benjamin Lindley
Benjamin Lindley

Reputation: 103703

Yes, the numbers are likely too big. On the most common systems nowadays, int is 32 bits, and its max value is 2^31-1, although it's only guaranteed to be 2^15-1 (requiring 16 bits). You can check your limits with:

#include <limits>
#include <iostream>

int main()
{
    std::cout << std::numeric_limits<int>::max();
}

In order to guarantee representation for values that large, you can use long long. unsigned long will do too, but barely. If you need integers of a specific size, I recommend you take a look at the <cstdint> header.

Upvotes: 2

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