C++ Terminate Called 'std::length_error'?

Question

Here is the error I get:

terminate called after throwing an instance of 'std::length_error'

what(): basic_string::_S_create

Aborted (core dumped)

I am reading a file that has about 50 lines. Do you see the issue in my code below?

using namespace std;

bool areParenthesesBalanced(const std::string& expr)
{
    stack<char> s;
    char a, b, c;

    for (int i=0; i<expr.length(); i++)
    {
        if (expr[i]=='(' || expr[i]=='[' || expr[i]=='{')
        {
            s.push (expr[i]);
        }
        else
        {
            switch (expr[i])
            {
                case ')':
                a = s.top();
                s.pop();
                if (a=='{' || a=='[')
                cout<<"Not Balanced";
                break;

                case '}':
                b = s.top();
                s.pop();
                if (b=='(' || b=='[')
                cout<<"Not Balanced";
                break;

                case ']':
                c = s.top();
                s.pop();
                if (c=='(' || c=='{')
                cout<<"Not Balanced";
                break;
            }
        }
    }

    if (s.empty())  //check if stack is empty
    {
        return true;
    }
    else
    {
        return false;
    }
}

int main()
{
    std::ifstream t("prog1.cpp");
    std::string str;
    t.seekg(0, std::ios::end);
    str.reserve(t.tellg());
    t.seekg(0, std::ios::beg);
    str.assign((std::istreambuf_iterator<char>(t)), std::istreambuf_iterator<char>());

    if(areParenthesesBalanced(str))
    {
        cout<<"Balanced";
    }
    else
    {
        cout<<"Not Balanced";
    }
    return 0;
}

You can't get the `top` from the stack, or `pop` it, if the stack is empty. You need to add a check for that. — Some programmer dude, Jul 23 '17 at 20:02
@TevinTwoTimes Don't for get to accept the answer, please. It solves your problems. — LogicStuff, Jul 25 '17 at 12:59

LogicStuff · Answer 1 · 2017-07-23T20:14:59.093

Your question:

To do std::string::assign, the string needs to be resized to be able to contain that range, not reserved. std::string::append or std::copy with std::back_inserter would work, though.

Something else:

You are not checking whether the stack is empty before accessing/popping its top element.

And maybe you want to return something, instead of doing cout<<"Not Balanced"; in areParenthesesBalanced.

Not errors:

^{You can make the loop contain only the switch statement.}

^{I don't think you need any of a, b and c variables. You should pop after all comparisons with std::stack::top.}

^{Lastly, please write return s.empty(); instead of six more lines.}

score 0 · Answer 2 · answered Jul 23 '17 at 20:10

If the stack is empty it will throw error. Please put a condition before using that. Also a little correction to your code. This might work...

using namespace std;

    bool areParenthesesBalanced(const std::string& expr)
    {
        stack<char> s;
        char a, b, c;

        for (int i=0; i<expr.length(); i++)
        {
            if (expr[i]=='(' || expr[i]=='[' || expr[i]=='{')
            {
                s.push (expr[i]);
            }
            else
            {
                switch (expr[i])
                {
                    case ')':
                    a = s.top();
                    s.pop();
                    if (a=='{' || a=='[')
                    cout<<"Not Balanced";
                    break;

                    case '}':
                    b = s.top();
                    s.pop();
                    if (b=='(' || b=='[')
                    cout<<"Not Balanced";
                    break;

                    case ']':
                    c = s.top();
                    s.pop();
                    if (c=='(' || c=='{')
                    cout<<"Not Balanced";
                    break;
                }
            }
        }

        if (s.empty())  //check if stack is empty
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    int main()
    {
        std::ifstream t("prog1.cpp");
        std::string str;
        t.seekg(0, std::ios::end);
        str.resize(t.tellg());
        t.seekg(0, std::ios::beg);
        str.assign((std::istreambuf_iterator<char>(t)), std::istreambuf_iterator<char>());

        if(areParenthesesBalanced(str))
        {
            cout<<"Balanced";
        }
        else
        {
            cout<<"Not Balanced";
        }
        return 0;
    }

C++ Terminate Called 'std::length_error'?

2 Answers2