Validate console input in c++

Question

I wrote the code below which works in a case of valid input

char input[100];
cin.getline(input, sizeof(input));
stringstream stream(input);
while (stream.rdbuf()->in_avail() != 0) {
    int n;
    stream >> n;
    numbers.push_back(n);
}

but fails when I put something instead of a number. How can I hadle wrong intput(e.g. any letter)?

I think you need to iterate the string input to check if it is composed only of integer digits before reading it into n — Mukul Gupta
– Mukul Gupta, Commented Jun 5, 2016 at 17:10
Possible duplicate of stackoverflow.com/questions/4654636/… — Mukul Gupta
– Mukul Gupta, Commented Jun 5, 2016 at 17:13
Possible duplicate of integer input validation, how?, Good input validation loop using cin - C++ — GingerPlusPlus
– GingerPlusPlus, Commented Jun 5, 2016 at 17:18

paweldac · Accepted Answer · 2016-06-05 17:15:43Z

1

For example:

bool is_number(const std::string& s)
{
    return !s.empty() && std::find_if(s.begin(), 
        s.end(), [](char c) { return !std::isdigit(c); }) == s.end();
}

foo() {
    char input[100];
    cin.getline(input, sizeof(input));
    stringstream stream(input);
    while (stream.rdbuf()->in_avail() != 0) {
        std::string n;
        stream >> n;
        if(is_number(n)) {
            numbers.push_back(std::stoi(n));
        }
        else {
            std::cout << "Not valid input. Provide number" << std::endl;
        }
    }
}

int main()
{
    foo();
    return 0;
}

answered Jun 5, 2016 at 17:15

paweldac

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2 Comments

djaszak Over a year ago

Thanks. You forgot #include<algorithm>

paweldac Over a year ago

@djaszak You're welcome. True I didn't write any includes.

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