Multidimentional array

Ducky · 11-01-2009, 09:42 AM

Im trying to strcat() text[] into buffer[] but i get an error.

What am i doing wrong?

Code:

#include <iostream>
using namespace std;

int main()
{
    int  c = 5;
    char text[3] = {'Hello','brave','world!'};
    char **dynamicArray = 0,  buffer[256] = {0};

    dynamicArray = new char *[c];

    for( int i = 0 ; i < c ; i++ )
         dynamicArray[i] = new char[3];

    for( int i = 0 ; i < 3 ; i++ )
    {
         strcat(buffer, text[i]);
    }
    cout << buffer << endl;

    //free the allocated memory
    for( int i = 0 ; i < c ; i++ )
    delete [] dynamicArray[i] ;
    delete [] dynamicArray ;

    return 0;
}

**laserlight** · 11-01-2009, 09:47 AM

Recall that character literals are single quoted, but string literals are double quoted, and a string literal is convertible to a pointer to its first element. As such, this:

Code:

char text[3]  = {'Hello','brave','world!'};

should be:

Code:

const char* text[3]  = {"Hello", "brave", "world!"};

By the way, you should just remove the whole deal concerning dynamicArray since it is not relevant to what you are asking about.

Elysia · 11-01-2009, 09:56 AM

Also recall that 3 characters are not enough to hold the strings. Furthermore, you use strcat on an uninitialized string.
I would just use a vector of vector instead of new, however. And std::string for that matter.

Ducky · 11-01-2009, 10:29 AM

Thank you very much Laselight and Eysia!

>>and a string literal is convertible to a pointer to its first element.

I didnt know that, its very useful, thanks.

>>you should just remove the whole deal concerning dynamicArray

Yes its not relevant but thats what im trying to learn and its in the process.
I think we cant change the title of the thread so if you have the power you can rename it if you want.

>>Also recall that 3 characters are not enough to hold the strings.

I thought they were 3 elements.

>>Furthermore, you use strcat on an uninitialized string.

Which one is uninitialized? buffer[256] is initialized to 0.

>>I would just use a vector of vector instead of new, however. And std::string for that matter.

Would it still be dynamic with vectors because i would need dynamic allocation.

Elysia · 11-01-2009, 10:54 AM

Quote:

Originally Posted by Ducky

>>Also recall that 3 characters are not enough to hold the strings.

I thought they were 3 elements.

3 elements of 1 char, yes.
We have the inner layer and the outer layer.
The outer layer specifies the number of strings you want and the inner layer specifies the maximum length of the string you want.

Quote:

>>Furthermore, you use strcat on an uninitialized string.
Which one is uninitialized? buffer[256] is initialized to 0.

Ah, but you are doing it on buffer. Of course, of course. I did not see that. No problem then.

Quote:

>>I would just use a vector of vector instead of new, however. And std::string for that matter.

Would it still be dynamic with vectors because i would need dynamic allocation.

vector would handle the dynamicness of the array. If you want to try making dynamic arrays yourself, I would not use it, I suppose.

Ducky · 11-01-2009, 11:10 AM

Cool, thank you!

I go with vectors if you say that its preferable.

Elysia · 11-01-2009, 01:29 PM

Yes, of course, it is more preferable than native arrays since it is less error prone, meaning safer programs and usually less development time due to less testing and debugging. But you will not learn anything about manual managing of dynamic arrays if that is what you want.

11-01-2009, 09:47 AM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 11,344	Recall that character literals are single quoted, but string literals are double quoted, and a string literal is convertible to a pointer to its first element. As such, this: Code: char text[3] = {'Hello','brave','world!'}; should be: Code: const char* text[3] = {"Hello", "brave", "world!"}; By the way, you should just remove the whole deal concerning dynamicArray since it is not relevant to what you are asking about. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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11-01-2009, 10:29 AM	#4
Ducky Registered User Join Date: Dec 2007 Location: France Posts: 431	Thank you very much Laselight and Eysia! >>and a string literal is convertible to a pointer to its first element. I didnt know that, its very useful, thanks. >>you should just remove the whole deal concerning dynamicArray Yes its not relevant but thats what im trying to learn and its in the process. I think we cant change the title of the thread so if you have the power you can rename it if you want. >>Also recall that 3 characters are not enough to hold the strings. I thought they were 3 elements. >>Furthermore, you use strcat on an uninitialized string. Which one is uninitialized? buffer[256] is initialized to 0. >>I would just use a vector of vector instead of new, however. And std::string for that matter. Would it still be dynamic with vectors because i would need dynamic allocation. __________________ Using Code::Blocks,MingW with Windows. Last edited by Ducky; 11-01-2009 at 10:32 AM.
Ducky is online now

11-01-2009, 11:10 AM	#6
Ducky Registered User Join Date: Dec 2007 Location: France Posts: 431	Cool, thank you! I go with vectors if you say that its preferable. __________________ Using Code::Blocks,MingW with Windows.
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