pointer to pointer troubles

[Alessio]

Hi,

I've a function that returns a pointer of a bidimensional array.

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int **foo(int *iSize); // iSize returns number of rows

I use it in this way...

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int i = 0;
int **lpiArray = foo(&i);

...and it runs perfectly.
The code that foo function uses for allocate memory for the array is this:

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int **lpiResult = malloc(10*sizeof(int*));
if ( NULL == lpiResult )
{
return NULL;
}

for ( i = 0; i < 10; i++ )
{
lpiResult[i] = malloc(2*sizeof(int));
if ( NULL == lpiResult[i] )
{
free(lpiResult);
return NULL;
}
}

My question is, why I can't pass a pointer for the bidimensional array instead of get it from function return ?
Something like:

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int foo(int **lpiArray); // function returns number of rows

and used in this way:

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int **lpiResult = NULL;
int iRows = foo(lpiResult);

Thanks!

[DMac]

Good News, you can.

Here is an example to Illustrate how it is done.

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#include <stdio.h>
#include <string.h>
#include <stdlib.h>

/****************************************************************************
*                                                                          *
* Function: Split (Perl's "split" function for C)                          *
*                                                                          *
* Purpose: Given a string and delimiter of any length returns an array of  *
* strings which are tokens that are separated by the delimiter in the      *
* original string. The original string is not touched. This emulates the   *
* functionality of Perl's "split" function (minus the use of regular       *
* expressions).                                                            *
*                                                                          *
****************************************************************************/

char** Split(char *Input, char *Delim, char ***List, int *TokenCount)
{
int Found, Length, DelimLen = strlen(Delim);
char *Remain, *Position;

if ((List == NULL) || (Input == NULL) || (Delim == NULL))
{
*TokenCount=-1;
return NULL;
}

//first pass -- count number of delimiters
for (Found = 1, Remain = Input;
(Position = strstr(Remain, Delim));
Found++) Remain = Position + DelimLen;

//create array based on number of delimiters
*List = (char **)malloc((Found+1) * sizeof(char *));

//second pass -- populate array
for (Found = 0,Remain = Input;
(Position = strstr(Remain, Delim),1);
Remain = Position + DelimLen)
{
Length = Position? Position - Remain : strlen(Remain);
(*List)[Found] = (char *)malloc(sizeof(char)*(Length+1));
strncpy((*List)[Found], Remain, Length);
(*List)[Found++][Length] = 0;
if(!Position){(*List)[Found] = Position; break;}
}

*TokenCount = Found;

return *List;
} /* Split() */


/* Destroys the array of strings structure returned by Split() */
void FreeSplitList(char **List)
{
int Count = 0;
while(List[Count]) free(List[Count++]);
free(List);

} /* FreeSplitList() */

/****************************************************************************
*                                                                          *
* Function: main                                                           *
*                                                                          *
* Purpose : Main entry point.                                              *
*                                                                          *
* History : Date      Reason                                               *
*           00/00/00  Created                                              *
*                                                                          *
****************************************************************************/

int main(int argc, char *argv[])
{
char *str = "The Quick Brown Fox Jumpped Over The Lazy Dogs";
char **strList;
int iCount;

Split(str," ",&strList,&iCount);

for(int i=0; i<iCount;i++)
{
printf("%s \n", strList[i]);
}

FreeSplitList(strList);

    return 0;
}



[Alessio]

Thank you, but this applies to one-dimensional arrays.
I would to understand how it can works with bidimensional arrays.

[DMac]

In the example the array of Tokens is in fact an array of character arrays.  You could apply this method to an array of Int arrays or whatever.

[Alessio]

In the example the array of Tokens is in fact an array of character arrays.  You could apply this method to an array of Int arrays or whatever.

Holy crap! What a shame!

Thanks !