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Dynamic allocation

Hi all

Im not quite sure how to use the new and delete for a whole array
dynamically.
Actually i want that, a user inputs a char in a single char array.
Everytime he inputs a char he creates a new array of (previous size +
1), he then copies the content of the old array in to the new array
and adds the new input at the end and deletes the old array. I guess
he has to pass the pointer to the array everytime.

For example.
input: a
output a
input: b
output: a b
input c:
output a b c .

Any clues??????????????

Feb 13 '07 #1
12 2089
"wh*************@gmail.com" <wh*************@gmail.comwrote in
news:11**********************@a75g2000cwd.googlegr oups.com:
Hi all

Im not quite sure how to use the new and delete for a whole array
dynamically.
Actually i want that, a user inputs a char in a single char array.
Everytime he inputs a char he creates a new array of (previous size +
1), he then copies the content of the old array in to the new array
and adds the new input at the end and deletes the old array. I guess
he has to pass the pointer to the array everytime.

For example.
input: a
output a
input: b
output: a b
input c:
output a b c .

Any clues??????????????

Forget arrays. Look up std::vector.
Feb 13 '07 #2
wh*************@gmail.com wrote:
Hi all

Im not quite sure how to use the new and delete for a whole array
dynamically.
Actually i want that, a user inputs a char in a single char array.
Everytime he inputs a char he creates a new array of (previous size +
1), he then copies the content of the old array in to the new array
and adds the new input at the end and deletes the old array. I guess
he has to pass the pointer to the array everytime.

For example.
input: a
output a
input: b
output: a b
input c:
output a b c .

Any clues??????????????
char* array = new char[sizeof_of_array];

delete[] array;

But Andre is right use std::vector or std::string. Forget memory
allocation details and learn how to program.

john
Feb 13 '07 #3
Try that:

#include<vector>
#include<iostream>
using namespace std;

vector<charvc;
char my_char;
for(;;;)
{
cin >my_char;
vc.push_back(my_char);
for(int i = 0; i < my_char.size(); i++)
{
cout << my_char[i] <<" ";
}
cout << endl;
}

Feb 13 '07 #4
On Feb 13, 2:00 am, John Harrison <john_androni...@hotmail.comwrote:
whitehatmira...@gmail.com wrote:
Hi all
Im not quite sure how to use the new and delete for a whole array
dynamically.
Actually i want that, a user inputs a char in a single char array.
Everytime he inputs a char he creates a new array of (previous size +
1), he then copies the content of the old array in to the new array
and adds the new input at the end and deletes the old array. I guess
he has to pass the pointer to the array everytime.
For example.
input: a
output a
input: b
output: a b
input c:
output a b c .
Any clues??????????????

char* array = new char[sizeof_of_array];

delete[] array;

But Andre is right use std::vector or std::string. Forget memory
allocation details and learn how to program.
Wellll.....not quite. Having a firm grasp on memory allocation/
deallocation is a Good Thing (TM) to have in *any* programming
language. Yes, even if that language is garbage collected and you
never have to worry about the specifics.

You don't necessarily need to learn the finer details of memory paging
and cache hits vs misses but being able to write a function that is
capable of dynamically reallocating an array is IMHO something that
every programmer should know regardless of language. If you lose sight
of things like this you won't realize why your program is leaking
copius amounts of memory and you'll end up with bad software.

That little tirade out of the way, once you learn enough about memory
allocation/deallocation/reallocation using classes like std::vector or
std::string is great and even recommended. They save you the time of
writing those classes yourself. They're *thouroughly* tested and
stable. All signs of good code.
john
Back to the original posting though,
Im not quite sure how to use the new and delete for a whole array
dynamically.
Syntax for new'ing an array is like this:

int array[] = new int[array_size] ;

Syntax for deleting an array is like:

delete [] array ;
I guess
he has to pass the pointer to the array everytime.
Well, if you're not passing the array into the method somehow
( explicit argument, member variable of a class, etc ) you're going to
have a hard time modifying it.

A non-C++ method signature for doing something like this would be:

int
add_member( char array[], int current_size ) ;

In 'real' C++ this would be accomplished using a std::vector or some
other container as mentioned.

HTH,
Paul Davis

Feb 13 '07 #5
On 13 Feb, 09:14, Angelina_Novach...@yahoo.com wrote:
Try that:

#include<vector>
#include<iostream>
using namespace std;

vector<charvc;
char my_char;
for(;;;)
{
cin >my_char;
vc.push_back(my_char);
for(int i = 0; i < my_char.size(); i++)
i < vc.size()

In this loop, i should probably be std::vector<char>::size_type. My
personal preference would be for pre-increment, rather than post-
increment too, although in this case it makes no difference in
practice.
{
cout << my_char[i] <<" ";
cout << vc[i] <<" ";

Gavin Deane

Feb 13 '07 #6
On 13 Feb, 09:20, "paul.joseph.da...@gmail.com"
<paul.joseph.da...@gmail.comwrote:
That little tirade out of the way, once you learn enough about memory
allocation/deallocation/reallocation using classes like std::vector or
std::string is great and even recommended. They save you the time of
writing those classes yourself. They're *thouroughly* tested and
stable. All signs of good code.
Any competent C++ programmer should of course know how to answer the
OP's question using new[] and delete[] explicitly (and should know to
use a container in preference). However, there is no need for someone
learning C++ to wait until they understand how to answer the question
the hard way before learning how to use standard containers to answer
the question the easy way. I expect that is what Andre Kostur and John
Harrison were getting at when they suggested std::vector to the OP.

The one time that advice isn't helpful of course, is when the OP is
doing this specifically to learn about new[] and delete[]. But that
wasn't mentioned as a specific goal. From what was written, the OP
could equally well have been using manual memory management simply
because they didn't know there was a better way.

Gavin Deane

Feb 13 '07 #7
On Feb 13, 4:50 am, "Gavin Deane" <deane_ga...@hotmail.comwrote:
On 13 Feb, 09:20, "paul.joseph.da...@gmail.com"

<paul.joseph.da...@gmail.comwrote:
That little tirade out of the way, once you learn enough about memory
allocation/deallocation/reallocation using classes like std::vector or
std::string is great and even recommended. They save you the time of
writing those classes yourself. They're *thouroughly* tested and
stable. All signs of good code.

Any competent C++ programmer should of course know how to answer the
OP's question using new[] and delete[] explicitly (and should know to
use a container in preference). However, there is no need for someone
learning C++ to wait until they understand how to answer the question
the hard way before learning how to use standard containers to answer
the question the easy way. I expect that is what Andre Kostur and John
Harrison were getting at when they suggested std::vector to the OP.

The one time that advice isn't helpful of course, is when the OP is
doing this specifically to learn about new[] and delete[]. But that
wasn't mentioned as a specific goal. From what was written, the OP
could equally well have been using manual memory management simply
because they didn't know there was a better way.

Gavin Deane
I guess I didn't specify clearly enough that my response was aimed at
this line:

'Forget memory allocation details and learn how to program.'

Which translates to: "Forget how to add and subtract numbers, use a
calculator instead."

Personally, I'd rather teach someone to fish than be stradled with
fishing for them.

Paul Davis

Feb 13 '07 #8

pa***************@gmail.com wrote: >>
>
Syntax for new'ing an array is like this:

int array[] = new int[array_size] ;
int *array = new int[array_size] ;

--
Maksim A. Polyanin

"In thi world of fairy tales rolls are liked olso"
/Gnume/
Feb 13 '07 #9
Actually i have just shifted from c to c++. I have not yet encountered
vector, anyway letme see what i can do with all the info i got here,
ill get back when i have some more code written.

Thank you all of u.

PS: I like that saying
>>Personally, I'd rather teach someone to fish than be stradled with
fishing for them.

Feb 14 '07 #10
wh*************@gmail.com wrote:
Actually i have just shifted from c to c++. I have not yet encountered
vector, anyway letme see what i can do with all the info i got here,
ill get back when i have some more code written.

Thank you all of u.

PS: I like that saying
>>>Personally, I'd rather teach someone to fish than be stradled with
fishing for them.
Probably just based on the common saying: "Give a man a fish and you feed
him for a day; teach a man to fish and you feed him for a lifetime."

Feb 14 '07 #11
i guess the code gotta be somthing like this:

int counter = 0;

int main(){
clrscr();
cout<<"Input a character: ";
get_char();
getch();
return 0;
}

get_char(){
ch = getch();
counter ++;
while (ch != -1){ ///exit if usr inputs -1

for (int i = 0; i<counter; i++)
dyn_array[i] = old_array[i];

dyn_array[i+1] = ch;
delete[] old_array;
print_array(*ptr_to_dyn_array, counter)
}

print_array(*ptr, int){
for (int i = 0; i =<counter;i++){
}
}

Something like this ............!!!!!?????
Im confused.........?????????????

Feb 14 '07 #12
Rolf Magnus wrote:
wh*************@gmail.com wrote:
>PS: I like that saying
>>>Personally, I'd rather teach someone to fish than be stradled with
fishing for them.

Probably just based on the common saying: "Give a man a fish and you feed
him for a day; teach a man to fish and you feed him for a lifetime."
Of course, there's the alternate version: "Give a man a fish, and you
feed him for a day; teach him to fish, and you give up your monopoly on
fisheries."

Feb 14 '07 #13

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