Dyanmic Array

To reiterate: the buffer-overflow problem is the main reason why you should avoid C-style arrays (whether on the stack or the heap) and use proper container classes that manage memory for you.

The key point about my method is that the size of the array is decided at run time, not at compile time. You could of course do some calculations to determine nSize and create whatever size you want. When copying to this dynamic array you should use safe, truncating copy functions like _snprintf or strncpy, not sprintf or strcpy (or memcpy for other types).

You method does not work. It is very bad programming. You are creating a single character and trying to use it as an array. You might as well write

char* s = 0x01234567;
cin>>s;

Both will work and in both cases you are writting memory you are not ment to modify.

And you are right, there are problems with this method and it can be difficult to use, which is why the vector template was created.

Quote:

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Originally posted by mwilliamson
The key point about my method is that the size of the array is decided at run time, not at compile time. You could of course do some calculations to determine nSize and create whatever size you want.

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//Edit: I got the picture. I went back and successful did the program using dynamic arrays and it worked.

Quote:

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Your method does not work. It is very bad programming. You are creating a single character and trying to use it as an array. You might as well write

char* s = 0x01234567;
cin>>s;

Both will work and in both cases you are writting memory you are not ment to modify.

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Yep, I know. Just learning.

Quote:

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And you are right, there are problems with this method and it can be difficult to use, which is why the vector template was created.

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Yeah, I am discovering that not everything I am learning is good use. Again the term "dynamic array" threw me off and let me to expect more. So, for now I am sticking to container class till I get a better hand at this.

Thanks for helping.

Code:

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#include <iostream>
#include <string>
#include <fstream>
#include <vector>

using namespace std;

typedef unsigned short int uShort;

int main()
{
        vector<char> vCh;
        char ch;
        char *arrayCh;

        cout<<"\nEnter the name of the file to read: \t";

        while(cin.get(ch))
        {
                if(ch == '\n')
                break;
                vCh.push_back(ch);
        }

        const uShort size = vCh.size();

        arrayCh = new char[size];

        for(uShort i=0; i<(uShort)vCh.size(); i++)
                arrayCh[i] = vCh[i];
       
        cout<<"\n\n";
        ifstream in(arrayCh);
        string s;
        while(getline(in, s))
        cout<<s <<"\n";
       
        delete[] arrayCh;
        arrayCh =0;

        return 0;
}

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The above is a sample working code of what I was trying to do.
I know I could have used:

Code:

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string inFile;
cin>>inFile;
ifstream in(inFile.c_str());

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... but it does not work well with file name with space in it.

The first code on top still has 3 issues:
1. The first issue is with cin.get(), I have to use cin.ignore(integer, '\n') if the code is in the middle of other operations to clean up the prompt.
2. How do I determine the size of the array arrayCh points to? (programmatically)
3. How can I be sure that nothing is being overriden as the array grows? I mean, what is the real mechanism being all this?

Ok, I know for a fact that the code is bad. I have found memory bugs in it.

There are problems if the file name is 1, 2, 4, 5, and 6 characters long - not 3 and above.

Trying to understand why.

c-cstrings need to be NULL terminated :

Code:

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arrayCh = new char[size+1];

for(uShort i=0; i<(uShort)vCh.size(); i++)
        arrayCh[i] = vCh[i];

arrayCh[size] = 0;

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Code:

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#include <iostream>
#include <string>
#include <fstream>

using namespace std;

int main()
{
    cout<<"\nEnter the name of the file to read: \t";

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

    ifstream in(inFile.c_str());

    if (in) cout << in.rdbuf() << endl;
   
    return 0;
}

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Thanks for the help.
I know your code works, but I have a need to solve the problem using dynamic arrays. My implementation of dynamic array in the above code is problematic at best. I am looking for someone to tell me why the code is shaddy.

And yes I forgot about "arrayCh = new char[size+1];", but the memory issues are still not solved.

Is the code below overriding memory it is not supposed to?

Code:

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for(uShort i=0; i<(uShort)vCh.size(); i++)
        arrayCh[i] = vCh[i];

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Looking at this code:

const uShort size = vCh.size();
arrayCh = new char[size];
for(uShort i=0; i<(uShort)vCh.size(); i++)
arrayCh[i] = vCh[i];

For one, you should use your size variable in the loop. While vCh.size() is unlikely to change, if it did you would have a buffer overflow. Plus, there is no reason to calculate the size every iteration of the loop. Especially when you have it stored!

I don't see anything immediately wrong with the code, maybe you could tell me what you mean by memory errors.

Quote:

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Originally posted by mwilliamson
Looking at this code:

const uShort size = vCh.size();
arrayCh = new char[size];
for(uShort i=0; i<(uShort)vCh.size(); i++)
arrayCh[i] = vCh[i];

For one, you should use your size variable in the loop. While vCh.size() is unlikely to change, if it did you would have a buffer overflow. Plus, there is no reason to calculate the size every iteration of the loop. Especially when you have it stored!

I don't see anything immediately wrong with the code, maybe you could tell me what you mean by memory errors.

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I know about vCh.size() in the for loop. I did that to test something.

If you compile and run the code below, which is essentially the same code as the original and enter a file name that is 1, 2, 4, 5, and 6 character long, you will get an error. I have inserted a series of cout in order to determine the root of the problem. So, take a look at the output and you might see the root cause of the problem.

Code:

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#include <iostream>
#include <string>
#include <fstream>
#include <vector>

using namespace std;

typedef unsigned short int uShort;

int main()
{
        vector<char> vCh;
        char ch;
        char *arrayCh;

        cout<<"\nEnter a choice: \t";

        while(cin.get(ch))
        {
                if(ch == '\n')
                break;
                vCh.push_back(ch);
                cout<<ch <<endl; //checking
        }

        const uShort size = vCh.size();
        cout<<"size = " <<size <<endl;      //checking
        cout<<"size = " <<vCh.size() <<endl; //checking

        arrayCh = new char[size + 1];

        cout<<"arrayCh = " <<sizeof(arrayCh) <<"\tcontent: " <<arrayCh <<"\t\taddress: " <<&arrayCh <<endl;//checking
        cout<<"arrayCh[] = " <<sizeof(arrayCh[size]) <<"\tcontent: " <<arrayCh[size] <<"\t\taddress: " <<&arrayCh[size] <<endl;

        for(uShort i=0; i<(uShort)vCh.size()/*(size)checking*/; i++)
                arrayCh[i] = vCh[i];

        cout<<"arrayCh = " <<sizeof(arrayCh) <<"\tcontent: " <<arrayCh <<"\taddress: " <<&arrayCh <<endl;//checking
        cout<<"arrayCh[] = " <<sizeof(arrayCh[size]) <<"\tcontent: " <<arrayCh[size] <<"\t\taddress: " <<&arrayCh[size] <<endl;

        cout<<"\n\n";
        ifstream in(arrayCh);
        string s;
        while(getline(in, s))
        cout<<s <<"\n";

        delete[] arrayCh;
        arrayCh =0;

        return 0;
}

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Here is the output when the file name is 2 characters (vc)

Code:

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E:\>dynamic

Enter a choice:        vc
v
c
size = 2
size = 2
arrayCh = 4    content: ─¥C    address: 1244660
arrayCh[] = 1  content: C      address: C
arrayCh = 4    content: vcC    address: 1244660
arrayCh[] = 1  content: C      address: C



E:\>

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As opposed to this when the file name is 3 characters long (cvc) or greater than 6 characters:

Code:

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E:\>dynamic

Enter a choice:        cvc
c
v
c
size = 3
size = 3
arrayCh = 4    content: ─¥C    address: 1244660
arrayCh[] = 1  content:        address:
arrayCh = 4    content: cvc    address: 1244660
arrayCh[] = 1  content:        address:


-VC

1-2 vc
2-1 c
3-0
4-3 -vc
5-2 vc
6-1 c
7-0
8-0
9-0
10-0
11-0

E:\>

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• you forgot to set the last character to NULL
  as in my previous post :
  
  
  Code:

  ---

  arrayCh = new char[size+1];

for(uShort i=0; i<(uShort)vCh.size(); i++)
        arrayCh[i] = vCh[i];

arrayCh[size] = 0;                // you forgot this line

  ---

• another way ... push NULL unto the vector array:
  
  
  Code:

  ---

      while(cin.get(ch))
    {
        if(ch == '\n')
        break;
        vCh.push_back(ch);
    }

    vCh.push_back(0);  // add this line

    const uShort size = vCh.size();

    arrayCh = new char[size];  // no need for + 1

    strcpy(arrayCh,&vCh[0]);    // note the syntax of using the vector

  ---

• even better, forget about the arrayCh completely :
  
  
  Code:

  ---

      while(cin.get(ch))
    {
        if(ch == '\n')
        break;
        vCh.push_back(ch);
    }

    vCh.push_back(0);  // add this line

    cout<<"\n\n";
    ifstream in(&vCh[0]);  // use the vector (again note syntax)

  ---

code1: does not work still (corrected arrayCh[size + 1] = 0;)
code2: works well <= still worry about memory being overriden somewhere
code3: works well <= but I needed dynamic array implementation in the code.

Do you know any better way of getting inputs off the command prompt than cin.get() and getline()?

Thanks a bunch for the help. :)