CODEWITHSUNDEEP
c++pointersoverwrite
greatfullgigapower
greatfullgigapower

Reputation: 3

How can you preserve the value of a pointer in c ++ without overwriting it

I Have this sandbox code for a proyect more complicated :

#include <sstream>
#include <iostream>
#include <vector>

using namespace std;

class Table
{
    friend class Variable;
public:
    Variable * variables[1021];
};

class Variable
{
    friend class Nodo;
public:
    char clas;
    Nodo * ini;
};

class Nodo
{   
public:
    char clas;
    Variable * father;
private:
    float * value;
public:
    Nodo();
    void set_value(float);
    float * get_value();
};


Nodo::Nodo()
{
    clas = ' ';
    father = NULL;
    value = NULL;
}

void Nodo::set_value(float m)
{
    float * r = new float();
    r = &m;
    value = (float *)r;
}

float * Nodo::get_value() 
{
    return this->value;
}

And this is the main:

void main ()
{
    Nodo * n = new Nodo();    // OK.
    n->set_value(5.3442);     // Ok. 

    Variable * v = new Variable();      // This is the problem.

    // When I declare another pointer an initilized it, n lost the value stored in value. 

    Variable * v0 = new Variable();   // Here the same.  
    v->ini = n;
    n->father = v;

    Table * t = new Table();
    t->variables[0] = v;

    v0 = t->variables[0];

    cout << *(static_cast<float *>(v0->ini->get_value())) << endl;
}

How can I stock the value in the pointer without change? It seems that I should use const, or something similar, but I don't know how. Declaring the field value as private doesn't help. The idea is replace value with a void * later, to store any king of basic date not only float data.

Thanks!

Upvotes: 0

Views: 800

Answers (1)

marcinj
marcinj

Reputation: 49986

This looks wrong:

void Nodo::set_value(float m)
{
    float * r = new float();
    r = &m;
    value = (float *)r;
}

r is assigned pointer to m which is a temporary, this pointer will be invalid once set_value finishes. Also you overwrite r value, so you have a leak here. The correct version would be:

void Nodo::set_value(float m)
{
    float * r = new float();
    *r = m;
    value = r;
}

btw. I am not digging deeper in your code, ...

Upvotes: 1

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