2D arrays. What's the difference?

[Nobody/Anonymous]

//////////////////////////////
Char **names = new char *[a];
for (int i = 0; i < a; i++)
{
   names[i] = new char[b];
}
//////////////////////////////
char *names[a];
for (int i = 0; i < a; i++)
{
   names[i] = new char[b];
}
/////////////////////////////
char names[a][b];
/////////////////////////////

Three ways to make a 2D array of chars using variables a and b. They all work fine.

The first one requires: delete [] names; when you're done with names. The others don't.

What's the difference? Is this really all allowed?

-Jay

[Nobody/Anonymous]

The difference is that in first case you created names with new, in other cases names is automatic object what would be deallocated when you return from function.

tkorrovi

[Nobody/Anonymous]

I thought in general you had to

delete [] array

or you were just clearing the pointer, not the array, but I am probably wrong and stupid.

Wayne

[Nobody/Anonymous]

I think I get it. I the first case the array will behave like one that was declared globally, in the other cases it will only be available within the function. right?

-Jay

-and thanks.

[Nobody/Anonymous]

Are you counting on dynamically allocated memory space to be freed when the variable goes out scope?

Wayne

[Nobody/Anonymous]

Here in C++. It is a 2D 'char' pointer-arrary.

#include <iostream>
#include <cstdlib>

     using namespace std;
    
char *name[][2] = {
  "item1", "Yes we have no bannas",
  "item2", "No we got bannas today",
  "item3", "maybe bannas another day",
  "", ""                                //   "item"   "maybe another day"
};                                     //   index         message
                                        //    ""    ,        ""  
                                        //    [0]            [1]
int main( )
  {
//  --------------------------------messages-----------------------------------
    cout << name[0][0] << endl;               // "item1"

      cout << name[1][0] << endl;               // "item2"
   
        cout << name[2][0] << endl << endl;       // "item3" 
      
// ---------------------------------indexes-----------------------------------

    cout << name[0][1] << endl;             // message1 "Yes we have no bannas"

      cout << name[1][1] << endl;             // message2 "No we got bannas today"
   
        cout << name[2][1] << endl << endl;     // message3 "maybe bannas another day"
                                               
//  ----------------------------------------------------------------------------      
   char str[80];
  int i;

  cout << "Enter keyword: ";
  cin >> str;                                               // item1  item2  item3
  for(i=0; *name[i][0]; i++)     //--indexes- step 1  creates: [0][0] [1][0] [2][0]
    if(!strcmp(name[i][0], str)) //--indexes- step 2  compares with string 'str'
      cout << name[i][1];        // prints message 'match' to screen ( note below )
                                                           // message1 message2 message3
     system("PAUSE > NUL");                                //  [0][1]   [1][1]   [2][1]
    return 0;
  }

N@N!

[Nobody/Anonymous]

Oh man sorry about the above post 'trash' !.
ok, here it is again.
Here in C++. It is a 2D 'char' pointer-arrary.

#include <iostream>
#include <cstdlib>

     using namespace std;
    
char *name[][2] = {
"item1", "Yes we have no bannas",
"item2", "No we got bannas today",
"item3", "maybe bannas another day",
"", ""                               
};                                    
                                       
                                       
int main( )
{

cout << name[0][0] << endl;               // "item1"

cout << name[1][0] << endl;               // "item2"
   
cout << name[2][0] << endl << endl;       // "item3" 
      

cout << name[0][1] << endl;             // message1 "Yes we have no bannas"

cout << name[1][1] << endl;             // message2 "No we got bannas today"
   
cout << name[2][1] << endl << endl;     // message3 "maybe bannas another day"
                                               

char str[80];
int i;

cout << "Enter keyword: ";
cin >> str;                                            
for(i=0; *name[i][0]; i++)    
if(!strcmp(name[i][0], str))
cout << name[i][1];       
                                                         
system("PAUSE > NUL");                               
return 0;
}

N@N!