c++ - object goes out of scope before = operation -

i have thous objects:

polygon p1, p2; 

and have inheriting class of polygon called triangle, , try do:

p1 = triangle(temp1, temp2, temp3); // temp 1,2,3 lengths of sides 

but reason destructor triangle called @ end of construction.

rectangle::~rectangle(void) {     polygon::~polygon(); }  polygon::~polygon(void) {     if (sides != null)     {         delete [] sides;         sides = null;     } } 

then runs destructor polygon second time.

so after code ends debugger says p1( n number of sides):

p1  {n=3 sides=0x0062c070 {-17891602} } polygon 

questions:

• why call destructor?
• why both triangle , polygon's destructor called?
• how can fixed?

edit: requested:

/*returns true if polygons , b: (a) each side on polygon there equal side on polygon b (b) number of sides in polygons , b equal (c) sum of sides of equals sum of sides of b */ bool polygon::operator==(const polygon& p) const {     if (n != p.n)         return false;     if(circumference() != p.circumference())         return false;     (int i=0; < n; i++)         if (!doessidehasequal(sides[i], p, n))             return false;     return true; } 

also, explanation why ran ~polygon, take account.

polygon p1;  p1 = triangle(temp1, temp2, temp3); // temp 1,2,3 lengths of sides 

is in fact giving result out of expectation.

what want

polygon& p1; triangle t(temp1, temp2, temp3);  p1 = t; 

or

polygon* p1 = new triangle(temp1, temp2, temp3); 

the problem in

p1 = triangle(temp1, temp2, temp3); 

is not triangle object temporary , destroyed right after statement, but, more seriously, copy triangle object p1 polygon, copying polygon. therefore, "copied" p1 not containing information of triangle.

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another problem way write destructor. destructor in c++ automatically chained (i think coming java background need explicitly invoke super class' finalizer)

rectangle::~rectangle(void) {     polygon::~polygon();  // can removed } 

therefore shouldn't call polygon's destructor.

another thing destructor is, if class supposed inherited (your polygon example), should declare destructor virtual. reason behind, search "virtual destructor".