Trying to access an index of an std::stack
c++, operators, stack, std, stl
Solution
`std::stack` doesn't inherit from the underlying container type, it adapts it to a completely new interface. The underlying container is not exposed. That's essentially the point of the adaptors `std::stack` and `std::queue`: they ensure that you're using a more limited interface that will be the same regardless of the underlying structures.
That said, you can inherit from `std::stack` and access the underlying container from a subclass. It is a `protected` member named `c`.
class my_stack : public std::stack< char > {
public:
using std::stack<char>::c; // expose the container
};
int main() {
my_stack blah;
blah.push( 'a' );
blah.push( 'b' );
std::cout << blah.c[ 1 ];
}
http://ideone.com/2LHlC7
Problem
``` void PDA::parse(vector<string> words){ for(int i=0; i<words.size();i++){//for each string in the input file string token=words[i]; for(int j=0; j<token.length(); j++) //for each character in the string { char input=token[j]; char matchingBracket=getMatchingBracket(input); //returns the matching bracket, should probably just have ( and [ if(!stack[j]){//since j-1 when the index is 0 will cause an error if(stack[j-1]==matchingBracket){ stack.pop(); }else{ stack.push(input); } } } accepted()?cout<<"The string "<<words[i]<<" is balanced and was accepted"<<endl : cout<<"The string "<<words[i]<<" is not balanced and was not accepted"<<endl; } } ``` I'm getting these errors ``` PDA.cpp:25: error: no match for âoperator[]â in â((PDA*)this)->PDA::stack[j]â PDA.cpp:26: error: no match for âoperator[]â in â((PDA*)this)->PDA::stack[(j - 1)]â ``` for these lines ``` if(!stack[j]){//since j-1 when the index is 0 will cause an error if(stack[j-1]==matchingBracket){ ``` I looked up std::stack and found out that "By default, if no container class is specified for a particular stack class, the standard container class template deque is used." When I looked up deque I found out it supports operator[]. This is how I declared my stack. In the corresponding header file to this source file. ``` #ifndef PDA_H #define PDA_H #include <stack> #include <vector> #include <deque> class PDA{ private: std::stack<char> stack; public: PDA(); bool isEmpty(); void parse(std::vector<std::string>); char getMatchingBracket(char); bool accepted(); }; #endif ``` As I see it, using operator[] on a std::stack should work just fine. Any ideas?