#include <sstream>
#include <iostream>

using namespace std;

int main()
{
    string s = "-123";
    
    int i;
    bool success;
    istringstream myStream(s);

    if (myStream>>i)
        success = true;
    else
        success = false;
    
    std::cout << success << std::endl;
    std::cout << i << std::endl;
}

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Converting string to int

c

C++