[c++] a problem with memory...

mamo139 (17)
i'm writing in c++ a class to manage matrixs.

matrici.h
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#include <cstdlib>
#include <iostream>

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#ifndef _MATRICI_H
#define _MATRICI_H 1

//**************** class ******************//

class matrice {
    public:
        int r;
        int c;
        double ** m;
        
        //costruttore e distruttore
        matrice();
        ~matrice();
        
        //crea matrice
        void create(int r, int c);
        void create_with_value(int r, int c, double value);
        
        //visualizza matrice
        void print();
        
        //caricamento - salvataggio matrici
        void load_from_file(char * file);
        void save_in_file(char * file);
        
        //operazioni su matrici
        friend matrice operator+(matrice, matrice);
        
        
};
    
#endif


matrici.cpp
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#include "matrici.h"

//costruttore
matrice::matrice(){
    r = 0;
    c = 0;    
}

//distruttore
matrice::~matrice(){
    
}

//creazione matrice
void matrice::create(int r, int c){ // r = righe, c = colonne

    int x,y;
     
    this->r = r;
    this->c = c;
    m = new double *[r];
    for(x=0;x<r;x++)
        m[x] = new double[c];

         
}
void matrice::create_with_value(int r, int c, double value){
    
    int x,y;
     
    this->r = r;
    this->c = c;
    m = new double *[r];
    for(x=0;x<r;x++)
        m[x] = new double[c];
            
    for(x=0;x<r;x++)
        for(x=0;x<r;x++)
            m[x][y] = value;
     
}

//visualizza matrice
void matrice::print(){
     
     int x,y;
     
     for(x=0;x<r;x++){
          for(y=0;y<c;y++)
               printf("%12.6f\x20",m[x][y]);
          printf("\n");     
     }
     printf("\n");
     
}

//caricamento - salvataggio matrici
void matrice::load_from_file(char * file){
    
    FILE *stream;
    char *buffer, *number;
    long filesize, readed;
    long x, y=0, mr=0, mc=0, r=0, c=0;

    stream = fopen(file,"rb");
    fseek(stream,0,SEEK_END);
    filesize = ftell(stream);
    rewind(stream);
    
    buffer = (char *) malloc(filesize * sizeof(char));
    number = (char *) malloc(100 * sizeof(char));
    readed = fread(buffer,1,filesize,stream);
    
    for(x=0; x<filesize ;x++){ //conta colonne
        if(buffer[x] == '\x09')
            mc++;
        if(buffer[x] == '\x0D'){
            mc++;
            break;
        }
    }
    for(x=0; x<filesize ;x++){ //conta righe
        if(buffer[x] == '\x0D')
            mr++;
    }
    
    create(mr, mc);
    
    for(x=0; x<filesize ;x++){
        if(buffer[x] == '\x0A')
            continue;
        if(buffer[x] == '\x09' || buffer[x] == '\x0D'){
            number[y] = '\x00';
            this->m[r][c] = atof(number);
            y=0;
            c++;
            if(buffer[x] == '\x0D'){
                r++;
                c=0;
            }
        }
        else{
            number[y] = buffer[x];
            y++;
        }
    }

}

void matrice::save_in_file(char * file){

    int x,y;
    FILE * stream;
    stream = fopen(file, "w+");
    
    for(x=0;x<r;x++){
        for(y=0;y<c;y++){
            fprintf(stream,"%.6f",m[x][y]);
            if(y<c-1) fprintf(stream,"\x09");
        }
        fprintf(stream,"\n");     
    }
    fclose(stream);

}

//operazioni su matrici
matrice operator+(matrice a,matrice b){
    
    matrice c;
    int x,y,i;
     
    if(a.r != b.r || a.c != b.c)
        exit(0);
     
    c.create(a.r, a.c);
     
     for(x=0;x<c.r;x++)
          for(y=0;y<c.c;y++)
               c.m[x][y] = a.m[x][y]+b.m[x][y];   

    return c;
}



we can try this class with this code
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#include "matrici.h"


int main(int argc, char *argv[])
{
    long x;

    matrice a,b;
    a.load_from_file("a.txt");
    a.save_in_file("b.txt");

    a.print();

    for(x=0;x<1000000000;x++)
        b = a + a;
    
    b.print();

    getchar();
    return 1;
}

this example shows very well the problem: doing 1000000000 times b=a+a; the memory used by the program increases a lot... i should find a way to free memory when i do not need it anymore.
but i don't know how to do it...

thank you very much,
Marco
Last edited on
R0mai (730)
delete stuff in your destructor.
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for(x=0;x<r;x++)
     delete[] m[x];
delete[] m;

mamo139 (17)
ok, i added delete stuff in my destructor
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matrice::~matrice(){
    
    int x;
    for(x=0;x<r;x++)
        delete[] m[x];
    delete[] m;
    
}


now there is a new problem...
i try this code
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#include "matrici.h"


int main(int argc, char *argv[])
{
    long x;

    matrice a,b;
    a.load_from_file("a.txt");
    a.save_in_file("b.txt");

    a.print();

    for(x=0;x<100000;x++)
    b = a + a;

    
    b.print();

    getchar();
    return 1;
}

and at runtime it give error...
because your code in the destructor after the operation b=a+a destroy all the arrays before the new loop, so it erase all the memory, also the one that i need...
Last edited on
R0mai (730)
I see the problem
You don't define a copy constructor and an assignment operator. So multiple objects use the same memory block.
Define 
 
 
matrice::matrice(const matrice& o);

and
 
 
matrice& matrice::operator=(const matrice& o);

Both of them should make a copy of the contents of o.m and copy them to this->m.

EDIT: also operator+ should take it's arguments by const references not by value. See the above function declarations for const references.
Last edited on
mamo139 (17)
ok... for matrice& operator=(const matrice& o); i tried in this way

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friend matrice operator=(matrice a);

matrice operator=(matrice a){
    
    int x,y;
    matrice b;
    
    b.create(a.r,a.c);
    
    for(x=0;x<a.r;x++)
          for(y=0;y<a.c;y++)
               b.m[x][y] = a.m[x][y];
               
    return b;
}


but my compiler (dev-c++) gives me theese errors...
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42 D:\Marco\MyProjects\matematica\classe matrici\matrici.h `matrice operator=(matrice)' must be a nonstatic member function 
42 D:\Marco\MyProjects\matematica\classe matrici\matrici.h `matrice operator=(matrice)' must take exactly two arguments 
136 D:\Marco\MyProjects\matematica\classe matrici\matrici.cpp `matrice operator=(matrice)' must be a nonstatic member function 
136 D:\Marco\MyProjects\matematica\classe matrici\matrici.cpp `matrice operator=(matrice)' must take exactly two arguments



and I do not understand what do you mean with matrice(const matrice& o);

sorry, it's just few days that i'm trying c++ (i usually use c) and so i not very good.

thanks a lot for your help ;)
Last edited on
R0mai (730)
Copy constructor should look like this:
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// in h file
class matrice {
//...
matrice(const matrice& o);
//...
}

//in cpp file:
matrice::matrice(const matrice& o) {
   
    create(o.r,o.c);
    for(int x=0;x<r;x++)
        for(int y=0;y<c;y++)
            m[x][y] = o.m[x][y];
}


Assigment operator shoudl look like this:
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// in h file
class matrice {
//...
matrice& operator=(const matrice& o);
//...
}

//in cpp file:
matrice& matrice::operator=(const matrice& o) {

    if (this == &o) { //We don't wanna copy ourselves into ourselves.
        return *this; //EDIT : added "*this"
    } 
    //deallocate current stuff
    for(x=0;x<r;x++)
        delete[] m[x];
    delete[] m;
    
    //allocate memory for new matrix, and copy the contents. 
    create(o.r,o.c);
    for(int x=0;x<r;x++)
        for(int y=0;y<c;y++)
            m[x][y] = o.m[x][y];

    return *this;
}


I haven't tested the code due to the lack of complier on this computer, so there could be syntax and other errors.


I hope you can use this example in the future on other classes you desing :)

Take care
Last edited on
mamo139 (17)
wow... now it works perfectly...
thank you very much for helping me!!

of course i will use your example when i will need it again, and now I study to understand all the things you taught me. :)

Marco
Last edited on
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