AddressSanitizer:DEADLYSIGNAL error on comparison

Question

I was trying to solve a leetcode problem of checking whether parenthesis are valid or not. While comparing a closing parenthesis to top element of stack I am encountering the following error. Also, error is occuring even when I am trying very obvious comparisons like 1>0. What is causing this error?

Error Description:
Runtime Error
AddressSanitizer:DEADLYSIGNAL
=

==33==ERROR: AddressSanitizer: SEGV on unknown address (pc 0x000000344919 bp 0x7ffdbedbbbf0 sp 0x7ffdbedbbac0 T0)
==33==The signal is caused by a READ memory access.
==33==Hint: this fault was caused by a dereference of a high value address (see register values below).  Dissassemble the provided pc to learn which register was used.
\#3 0x7f72702470b2  (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
AddressSanitizer can not provide additional info.
==33==ABORTING

class Solution {
public:
    bool isValid(string s) {
        char tmp;   
            stack <char> c_stack;
            char b10='(',b20='{',b30='[';
            char b11=')',b21='}',b31=']';
        for(int i=0;i<s.size();i++)
        {
            if(s[i]==b10||s[i]==b20||s[i]==b30)
            c_stack.push(s[i]);
            else
            {
                if(c_stack.empty())
                continue;
                tmp=c_stack.top();
                if(tmp==b10 && s[i]==b11)
                c_stack.pop();
                else if(tmp==b20 && s[i]==b21)
                c_stack.pop();
                else if(tmp==b30 && s[i]==b31)
                c_stack.pop();
                else
                break;             
            }
            cout<<c_stack.top();
            
        }
        return c_stack.empty();
        
    }
};

Answer 1

You push an opening delimiter onto the stack... When you should have the closing delimiter to match there.... And possibly some more information to pinpoint the error.

Also, never pass std::string's by value unless a fresh copy is absolutely needed, which is not the case for your needs.

Here one way to implement these tips into working code:

#include <algorithm>
#include <cassert>
#include <iostream>
#include <stack>
#include <string>
#include <string_view>

bool isValid(const std::string& s) {
    char tmp;
    std::stack<std::pair<const char*, size_t>> c_stack;

    // pair up delimiters, this wuill make matching easier to handle.
    static const char* delim_pairs[] = {"()", "[]", "{}"};

    for (size_t i = 0; i < s.length(); ++i) {
        const auto c = s[i];

        // check for opening delimiter
        bool match = false;
        for (auto& d : delim_pairs) {
            if (c == d[0]) {
                c_stack.push({d, i});
                match = true;
                break;
            }
        }
        // no use checking for more if a match was found.
        if (match) continue;

        // check for closing delimiter
        for (auto& d : delim_pairs) {
            if (c == d[1]) {
                if (!c_stack.empty()) {
                    // does it match?
                    if (!c_stack.empty() && c == c_stack.top().first[1]) {
                        c_stack.pop();
                        break;  // no use checking for more if a match was
                                // found.
                    }

                    // it doesn't match
                    std::cout << "Error: string: \"" << s
                              << "\" unmatched opening delimiter \'"
                              << c_stack.top().first[0]
                              << "\'' at position: " << c_stack.top().second
                              << "\n";
                    return false;  // no use checking for more if error
                } else {
                    std::cout << "Error: string: \"" << s
                              << "\" unmatched closing delimiter \'" << c
                              << "\'' at position: " << i << "\n";
                    return false;  // no use checking for more if error
                }
            }
        }
    }

    if (c_stack.empty()) return true;

    auto& err = c_stack.top();
    std::cout << "Error: string: \"" << s << "\" unmatched opening delimiter \'"
              << err.first[0] << "\'' at position: " << err.second << "\n";
    return false;
}

int main() {
    assert(isValid("1+1"));
    assert(isValid("(1+1)"));
    assert(isValid("[(1+2) - (1)] + 2"));
    assert(isValid("[(1+2) - {x}] [5,6] + 2"));
    assert(!isValid("(1+2)-{x}] [5,6] + 2"));
    assert(!isValid("(1+2)-x} [5,6] + 2"));
    assert(!isValid("("));
    assert(!isValid("([)"));
    assert(!isValid("([{]})"));

    return 0;
}

You can play with the above code here: https://godbolt.org/z/v1x5x67j8