问AddressSanitizer:使用堆栈运行代码时DEADLYSIGNAL错误

EN

AddressSanitizer:DEADLYSIGNAL
=================================================================
==30==ERROR: AddressSanitizer: SEGV on unknown address (pc 0x0000003783d6 bp 0x7ffe68231e10 sp 0x7ffe68231ca0 T0)
==30==The signal is caused by a READ memory access.
==30==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 0x7f427121b0b2  (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
AddressSanitizer can not provide additional info.
==30==ABORTING

#include <stack>

using namespace std;

class Solution {
public:
    bool isValid(string str) {
        stack<char> s;
        bool val=true;
        for(int i=0;i<str.length();i++){
            if(str[i]=='(') s.push(')');
            else if(str[i]=='{') s.push('}');
            else if(str[i]=='[') s.push(']');
            else if(str[i]==')'||str[i]=='}'||str[i]==']'){
                if(str[i]==s.top()) s.pop();
                else if(str[i]!=s.top()) {
                    val=false;
                    break;
                }
            }
        }
        if(s.empty()) val=true;
        else if(!s.empty()) val=false;
        
        return val;
    }
};