c++ - Polynomial++: How to increment p(x) by 1 -

i have polynomial class, , trying define operator++, both pre- , post- incrementation, trying define pre- , post- decrementation, namely operator--. here snippet of code:

class polynomial { public:     polynomial();     polynomial(vector<int>coeffs);     /*     .     .     .     */     polynomial operator++();     polynomial& operator++ (int unused);     polynomial operator--();     polynomial& operator-- (int unused);     /*     .     .     .     */  private:     vector<int> coefficient; };  polynomial polynomial::operator++() {     coefficient[0]++;     return *this; } polynomial& polynomial::operator++ (int unused) {     polynomial copy(*this);     coefficient[0]++;     return copy; } polynomial polynomial::operator--() {     coefficient[0]--;     return *this; } polynomial& polynomial::operator-- (int unused) {     polynomial copy(*this);     coefficient[0]--;     return copy; } 

i error when trying in main:

polynomial p(...some vector...);

cout << p++;

you returning references temporaries postfix operators:

polynomial& polynomial::operator++ (int unused) {     polynomial copy(*this);     coefficient[0]++;     return copy;     // returning reference local variable } 

this undefined behaviour. have return type of post , pre-increment wrong way around. need this:

polynomial& operator++(); polynomial operator++ (int); polynomial& operator--(); polynomial operator-- (int);