Unordered_map Find Function

S

Shashank_Choudhary

C++ Certificate Advanced C++ Certificate
Joined
1/21/19
Messages
313
Points
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Hi ,
'
I am trying to compile the following code ,
C++: 
std::unordered_map<char ,char> mappings = {{')', '('}, {'}' , '{'} , {']','['}};
        std::stack<char> Stack;
        for(int i = 0; i < s.length() ; ++i)
        {
            char c = s.at(i);
            if(mappings.find(c) != s.end()) // ERROR !!!
            {
            ...
            }
        }
I get the following error ,
Invalid operands to binary expression ('std::unordered_map<char, char>::iterator' (aka '__hash_map_iterator<__hash_iterator<std::__hash_node<std::__hash_value_type<char, char>, void *> *>>') and 'std::basic_string<char>::iterator' (aka '__wrap_iter<char *>'))

I think I am comparing the wrong iterators in the "if" loop but I don't see why ? Any help would be much appreciated.
Thank you :)
 
DiamondCorp said:
Hi ,
'
I am trying to compile the following code ,
C++: 
std::unordered_map<char ,char> mappings = {{')', '('}, {'}' , '{'} , {']','['}};
        std::stack<char> Stack;
        for(int i = 0; i < s.length() ; ++i)
        {
            char c = s.at(i);
            if(mappings.find(c) != s.end()) // ERROR !!!
            {
            ...
            }
        }
I get the following error ,
Invalid operands to binary expression ('std::unordered_map<char, char>::iterator' (aka '__hash_map_iterator<__hash_iterator<std::__hash_node<std::__hash_value_type<char, char>, void *> *>>') and 'std::basic_string<char>::iterator' (aka '__wrap_iter<char *>'))

I think I am comparing the wrong iterators in the "if" loop but I don't see why ? Any help would be much appreciated.
Thank you :)
Click to expand...
Yes, s.end() (which is the string) will never be the same iterator with the keyset in unordered. Compare it mappings.end() instead of s.end() will resolve this issue.
 
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