Dynamická alokace paměti – C / C++ – Fórum – Programujte.com

// Frosty edit: Tam, kde je naps?no [i.] to m? b?t bez t? te?ky. Upravil jsem to tak, proto?e F?rum to form?tuje jako kurz?vu.

Mrkn?te se na tento k?d:

#include <cstdlib>

#include <iostream>



using namespace std;



char* allocate_mem(char* c, int size) {

    char* a = new char[size];

    for(int i = 0; i != size; i++)

        a[i.] = c[i.];

    return c;

};



int main(int argc, char *argv[])

{

    char* pa = allocate_mem("abcdef", 6);

    cout << "Adresa 'pa': " << &pa << endl;

    char ca[10] = "abcdefghi";

    char* da = allocate_mem(ca, 10);

    cout << "Adresa 'da': " << &da << endl; //Vsimnete si rozdilu

    cout << "Hodnota 'da':" << da << endl;

    cout << "Adresa 'ca': " << &ca << endl;

    cout << "Hodnota 'ca':" << ca << endl;

    int ia[10];

    cout << "Adresa 'ia': " << ia << endl; //ALE !!!

    delete []pa;

    delete []da;

    char cdf[9] = "12345678";

    cout << "[del] Adresa 'da': " << &da << endl;

    cout << "[del] Hodnota 'da':" << da << endl;

    cout << "[del] Adresa 'ca': " << &ca << endl;

    cout << "[del] Hodnota 'ca':" << ca << endl;

    system("PAUSE");

    return EXIT_SUCCESS;

}

proto?e m?sto je uvoln?no pro dal?? alokace, resp pro dal?? pou?it?. Pokud ale pou?ito nebylo, lze ho teoreticky volat.

>> vol?n? dynamicky alokovan? prom?nn? po DELETE -> nedefinovan? chov?n

#include <cstdlib>

#include <iostream>



using namespace std;

// tady jste vytvoril docela pekny memory leak - protoze jste vracel retezec c misto a

char* allocate_mem(char* c, int size) {

    char* a = new char[size];

    int j;

    for(j = 0; j != size; j++)

        a[j] = c[j];

    a[j] = '\0';  // v C se ukoncuji retezce nulou    

    return a;//c;

};



int main(int argc, char *argv[])

{

    char* pa = allocate_mem("abcdef", 6);

    cout << "Adresa 'pa': " << &pa << endl;

    char ca[10] = "abcdefghi";

    char* da = allocate_mem(ca, 10);

    cout << "Adresa 'da': " << &da << endl; //Vsimnete si rozdilu

    cout << "Hodnota 'da':" << da << endl;

    cout << "Adresa 'ca': " << &ca << endl;

    cout << "Hodnota 'ca':" << ca << endl;

    int ia[10];

    cout << "Adresa 'ia': " << ia << endl; //ALE !!!

    delete []pa;

    delete []da;

    pa = da = 0; // po dealokaci je potreba priradit NULL 

    char cdf[9] = "12345678";

    cout << "[del] Adresa 'da': " << &da << endl;

    cout << "[del] Hodnota 'da':" << da << endl;

    cout << "[del] Adresa 'ca': " << &ca << endl;

    cout << "[del] Hodnota 'ca':" << ca << endl;

    system("PAUSE");

    return EXIT_SUCCESS;

}

Tak jsem trochu experimentoval:

#include <cstdlib>

#include <iostream>



using namespace std;



int main(int argc, char *argv[])

{

      char m = 'F';

      cout << m << endl;

      char* a = new char[70];

      int j;

      for(j = 0; j != 70; j++) 

            a[j] = 'X';

      a[j] = '';

      cout << &a << endl;

      char f[70];

      for(j = 0; j != 70; j++)

            f[j] = a[j];

      delete []a;

            //Nelze ozna?it jako voln? m?sto:

      delete []f;  // statick? prom?nn? 

            //Kompil?tor pouze upozorn?

      char* s = f;

      cout << &f << "  " << &s << "  " << &a << endl;

      cout << a << endl;

      cout << s << endl;

      cout << f << endl;

      int i(0);

      system("PAUSE");

      return 0;

}

d1ce napsal:

I když se kompilátoru dají nastavit různé parametry, stejně je pravděpodobná odpovědnost za volání smazaní, dynamicky alokované paměti na programátorovi.