How to deallocate a matrix

[Wei-Chao Hsu]

The program always crashs where the memory is deallocated. Any one could
help me? Thanks!

#include <iostream>

void main()
{
//Allocate
int **a=new int* [4];
for(int i=0;i<10;++i)
a[i]=new int [10];
for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
a[i][j]=100*i+j;

for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
std::cout<<a[i][j]<<std::endl;

//Deallocate
for(int i=0;i<4;++i)
delete [] a[i];
delete [] a; //crash at here!

}

[Robert Bauck Hamar]

In article <ca***********@news.ntust.edu.tw>, Wei-Chao Hsu wrote:

The program always crashs where the memory is deallocated. Any one could
help me? Thanks!

#include <iostream>

void main()
Should be int main()
{
//Allocate
int **a=new int* [4];
for(int i=0;i<10;++i)
Is 10 the correct number here?
a[i]=new int [10];
for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
a[i][j]=100*i+j;

for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
std::cout<<a[i][j]<<std::endl;

//Deallocate
for(int i=0;i<4;++i)
delete [] a[i];
delete [] a; //crash at here!
It probably has something to do with the first for loop writing to
memory it doesn't own.
}

A tip:
#include <vector>
#include <iostream>

int main()
{
//allocate
std::vector<std::vector<int> > a(4, std::vector<int>(10));
for (int i=0; i < a.size(); ++i)
for (int j=0; j < a[i].size(); ++j)
a[i][j] = 100*i+j;
for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
std::cout<<a[i][j]<<std::endl;

//deallocation: automatic
}

--
Robert Bauck Hamar

[Ian]

Wei-Chao Hsu wrote:

The program always crashs where the memory is deallocated. Any one could
help me? Thanks!

#include <iostream>

void main()
{
//Allocate
int **a=new int* [4];
for(int i=0;i<10;++i)
a[i]=new int [10];
Should that be for(int i=0;i<4;++i) ?

Ian
for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
a[i][j]=100*i+j;

for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
std::cout<<a[i][j]<<std::endl;

//Deallocate
for(int i=0;i<4;++i)
delete [] a[i];
delete [] a; //crash at here!

}

[Wei-Chao Hsu]

Wei-Chao > > //Allocate

int **a=new int* [4];
for(int i=0;i<10;++i)

Is 10 the correct number here?

It should be 4. Thanks!

[William Xuuu]

Robert Bauck Hamar <ro**********@ifi.uio.no> writes:

A tip:
#include <vector>
#include <iostream>

int main()
{
//allocate
std::vector<std::vector<int> > a(4, std::vector<int>(10));
for (int i=0; i < a.size(); ++i)
for (int j=0; j < a[i].size(); ++j)
a[i][j] = 100*i+j;
for(int i=0;i<4;++i)
for(int j=0;j<10;++j)
std::cout<<a[i][j]<<std::endl;

//deallocation: automatic
}

Hmmh, your tip seems good when dealing with two dimension arrays. I'm wondering
whether there're some similar methods dealing with three, four, five,
.... dimension arrays. Huh?

--
William Xuuu
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