Operator[] C++ Get/Set -

i'm having trouble telling difference between , set operator[]. need tell difference between these function calls.

cout << data[5]; data[5] = 1; 

i googled it, , answers found still didn't help. people suggested making signatures methods different adding const. did that, , still both called same method.

there signatures had used:

const t& operator[](unsigned int index) const; t& operator[](unsigned int index); 

what doing wrong?

the solution use "proxy" object delay actual operation:

#include <vector> #include <iostream>  template<typename t> struct myarray {     std::vector<t> data;     myarray(int size) : data(size) {}      struct deref {         myarray& a;         int index;         deref(myarray& a, int index) : a(a), index(index) {}          operator t() {             std::cout << "reading\n"; return a.data[index];         }          t& operator=(const t& other) {             std::cout << "writing\n"; return a.data[index] = other;         }    };     deref operator[](int index) {        return deref(*this, index);    } };  int main(int argc, const char *argv[]) {     myarray<int> foo(3);     foo[1] = 42;     std::cout << "value " << foo[1] << "\n";     return 0; } 

simple const-ness cannot used because may need read non-const instance, reason must delay operation: assignment happens "after" access , compiler doesn't tell if access later used target assignment or not.

the idea therefore on access store away index has been requested , wait know if reading or writing operation happening. providing implicit conversion operator proxy t know when reading operation occurs, providing , assignment operator proxy t know when writing occurs.