Dynamic Allocation of Memory

[omariqbalnaru@inbox.com]

Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?

[Victor Bazarov]

Re: Dynamic Allocation of Memory

omariqbalnaru@i nbox.com wrote:

Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?

There are different way of doing that. One is to ask the input for the
number of symbols available, then allocate, then read. Another is to
use 'std::string' and 'std::getline', which will fill the string with
the input dynamically expanding the string. Then you can query the
string for its contents.

What I think you should avoid using all means is dynamically allocating
memory yourself. Use standard containers and strings as much as you can.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Jim Langston]

Re: Dynamic Allocation of Memory

<omariqbalnaru@ inbox.comwrote in message
news:1164212117 .684426.108540@ j44g2000cwa.goo glegroups.com.. .

Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?

Well, a few ways, depending on your input. What are you inputing to?

A normal way would be to do:

std::string Name;
std::getline( std::cin, Name );

Now, the std::string internally contains a dynamic buffer. This is actually
doing what you are asking about in a container behind the scenes.

Now, if for some reason you need to store this Name in a char array instead
of a std::string, you could do this:

std::string Name;
std::getline( std::cin, Name );
// Remember we need to reserve one space for the null terminator
char* NameArray = new char[Name.length() + 1];
strcpy( NameArray, Name.c_str() );
// remember to delete[] the new allocated memory when done
delete[] NameArray;

It all depends on what you are actually trying to achieve. It sounds to me,
however, that std::string will work for you without having to use new
yourself.

[omariqbalnaru]

Re: Dynamic Allocation of Memory

How to use the string class while reading from an ifstream?

Jim Langston wrote:

<omariqbalnaru@ inbox.comwrote in message
news:1164212117 .684426.108540@ j44g2000cwa.goo glegroups.com.. .

Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?

>
Well, a few ways, depending on your input. What are you inputing to?
>
A normal way would be to do:
>
std::string Name;
std::getline( std::cin, Name );
>
Now, the std::string internally contains a dynamic buffer. This is actually
doing what you are asking about in a container behind the scenes.
>
Now, if for some reason you need to store this Name in a char array instead
of a std::string, you could do this:
>
std::string Name;
std::getline( std::cin, Name );
// Remember we need to reserve one space for the null terminator
char* NameArray = new char[Name.length() + 1];
strcpy( NameArray, Name.c_str() );
// remember to delete[] the new allocated memory when done
delete[] NameArray;
>
It all depends on what you are actually trying to achieve. It sounds to me,
however, that std::string will work for you without having to use new
yourself.

[omariqbalnaru]

Re: Dynamic Allocation of Memory

And please tell me that will it cater for the spaces too?

omariqbalnaru wrote:

How to use the string class while reading from an ifstream?
>
Jim Langston wrote:

<omariqbalnaru@ inbox.comwrote in message
news:1164212117 .684426.108540@ j44g2000cwa.goo glegroups.com.. .

Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?

Well, a few ways, depending on your input. What are you inputing to?

A normal way would be to do:

std::string Name;
std::getline( std::cin, Name );

Now, the std::string internally contains a dynamic buffer. This is actually
doing what you are asking about in a container behind the scenes.

Now, if for some reason you need to store this Name in a char array instead
of a std::string, you could do this:

std::string Name;
std::getline( std::cin, Name );
// Remember we need to reserve one space for the null terminator
char* NameArray = new char[Name.length() + 1];
strcpy( NameArray, Name.c_str() );
// remember to delete[] the new allocated memory when done
delete[] NameArray;

It all depends on what you are actually trying to achieve. It sounds to me,
however, that std::string will work for you without having to use new
yourself.

[Gavin Deane]

Re: Dynamic Allocation of Memory

Please do not top-post. Thank you. Rearranged.
omariqbalnaru wrote:

omariqbalnaru wrote:

Jim Langston wrote:

<omariqbalnaru@ inbox.comwrote in message
news:1164212117 .684426.108540@ j44g2000cwa.goo glegroups.com.. .
Is there anyway to allocate memory dynamically according to the input?
For example if the user has to input his name e.g. in this case Omar
Iqbal Naru is inputted by the user. How to allocate memory dynamically
to store this name in a character array including the spaces?
>
Well, a few ways, depending on your input. What are you inputing to?
>
A normal way would be to do:
>
std::string Name;
std::getline( std::cin, Name );

How to use the string class while reading from an ifstream?

Exactly the same way as the code above. The std::getline function works
with any kind of istream. std::cin is an istream and so is any ifstream
object. So just replace std::cin with the name of your ifstream object
in the above code and you have what you need.

And please tell me that will it cater for the spaces too?

It will. std::getline reads up to the line terminator which, by
default, is \n. So if the whole line is the input stream you read from
contains spaces, the whole line including spaces will be read.

Gavin Deane

[omariqbalnaru]

Re: Dynamic Allocation of Memory

I tried this:

string a;

getline(cin, a, '\n');

a string ends up being an empty string. Please help.

[omariqbalnaru]

Re: Dynamic Allocation of Memory

struct studentnode
{
string name;
int rollnumber;
studentnode *next;
studentnode *previous;
courselist *listofcourses;
};

coursenode c;

cout<<"Enter the name of the student followed by a full stop"<<endl;
getline(cin, s.name);
or
getline(cin, s.name, '\n');

both result in s.name ending up as an empty string.

[BobR]

Re: Dynamic Allocation of Memory


omariqbalnaru wrote in message
<1164820457.429 064.19990@14g20 00cws.googlegro ups.com>...

>struct studentnode{
string name;
int rollnumber;
studentnode *next;
studentnode *previous;
courselist *listofcourses;
};
>coursenode c;
>cout<<"Enter the name of the student followed by a full stop"<<endl;
>getline(cin, s.name);
>or
>getline(cin, s.name, '\n');
>both result in s.name ending up as an empty string.

Well, duh! 's.name' does not exist! <G>
There is something you are not telling.

Try this program, (console mode):

// -------
#include <iostream>
#include <ostream>
#include <sstream>
#include <string>

struct studentnode{
std::string name;
int rollnumber;
studentnode *next;
studentnode *previous;
// courselist *listofcourses; // non-existant
studentnode(std ::string const &nm) : name(nm){}
};

int main(){
std::istringstr eam siscin("Billybo b Quincy Humperdinger \n");

std::cout<<"Ent er the name of the student followed by a full stop"
<<std::endl;
std::string name;
std::getline( siscin, name );

std::cout<<" name ="<< name <<std::endl;

studentnode Sn( name );
std::cout<<" Sn.name ="<< Sn.name <<std::endl;

return 0;
} // main()
// -------

/* - output -
Enter the name of the student followed by a full stop
name =Billybob Quincy Humperdinger
Sn.name =Billybob Quincy Humperdinger
*/

If that works, comment-out the first line in main() (istringstream) and
change getline to:

std::getline( std::cin, name );

--
Bob R
POVrookie