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C++ STL list memory issues

1 New Member
This is for all those STL-heads out there, this mught be trivial for you but I am a noob with the STL. I am having to implement a system in which I wil have many (thousands) of containers, I have been noticing that once you delete an element from a list memory is not released until program termination.

for the sake of argument lets say that the code looks like:

#include <iostream>
#include <list>

using namespace std;

int main(int argc, char *argv[]){
list<int> tList;


for (int i=1; i<=500000; i++){
tList.push_back (i);
cout << "i: " << i << endl;
}

cout << "tList.fron t(): " << tList.front() << endl;
cout << "tList.back (): " << tList.back() << endl;

list<int>::iter ator Iter;
Iter = tList.begin();

// According to myself this is where I delete all elements in the list
tList.erase(Ite r, tList.end());


cout << "tList.fron t(): " << tList.front() << endl;
cout << "tList.back (): " << tList.back() << endl;



//hold for input
int c;

do
{
c = getchar();
if(c == EOF) break;
} while(c != '\n');

}//:~

but after looking at memory, all the memory taken up by the initialization is still allocated, Is there a way of releasing this memory?
Jul 21 '06 #1
2 6287
Banfa
9,065 Recognized Expert Moderator Expert
// According to myself this is where I delete all elements in the list
tList.erase(Ite r, tList.end());

The help for erase specifically says that no reallocation takes place (so that other pointers and iterators remain valid). If you want to clear you list why no use

tList.clear();

If you only want to remove a few elements then having removed the unwanted elements use

tList.resize( ... );

http://msdn2.microsoft.com/en-us/library/00k1x78a.aspx
Jul 22 '06 #2
sovedyr
1 New Member
I too have a problem with the allocation of memory when using list.

#define pi 3.1415926535897 932384626433832 795028841971693 9937510
#include <iostream>
#include <fstream>
#include <cmath>
#include <cstdlib>
#include <list>
#include <deque>
#include "rkstep.h"
#include "norm.h"
#include "rkdrive.h"

using namespace std;

void func(double x, double* y, double* f)
{
f[0] = y[1];
f[1] = -y[0];
}

int main()
{
int ny = 2;

double x = 0.0;
double y[] = {0.0,2.0};
double h = 0.001;
double eps=0.001;
double acc=0.001;

double b = 20.0;
double y1[ny];
double dy[ny];

rkstep(&func,x, y,ny,h,y1,dy);

list<double> xlist;
xlist.push_back (x);


list<double*> ylist;
ylist.push_back (y);

rkdrive(&func,& xlist,&ylist,ny ,b,acc,eps,h);

list<double*>:: iterator j;
list<double>::i terator i;

ofstream test1("test.dat ",ios::out) ;
for(i=xlist.beg in(),j=ylist.be gin(); j!=ylist.end(); i++, j++)
{
test1 << *i << " " << **j << "\n";
}
return 0;
}

where rkstep is a function who will change x and y then in rkdrive one numer is added to the xlist using the push_back, while the ylist gets an array added in the end so ylist is now a list of arrays.
Now in the for loop I want to return the values of xlist and ylist. This also works for 1999 out of 2000 entrances. but for the last one I get a random number indicating that the allocation of memory for the list is not done correctly.
How can I avoid this problem?

Cheers,
Sovedyr
May 12 '10 #3

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