Re: alloc

[Gary Polhill]

> Lorenzo wrote:
> 
> I'm a newbye in objective-C. If I write in c:
> 
> #include <stdio.h>
> #include <malloc.h>
> 
> int main();
> int main()
> {
>   int i, j;
>   int numCol[5]={8,8,8,9,10};
>   char *Ipezzo[5];
>   char **labelsHist;
> 
>   labelsHist=(char **) malloc(sizeof (char *) * 5);
>   for(i=0;i<5;i++)
>     {
>       Ipezzo[i]=(char *) malloc(sizeof (char) * 2);
>       labelsHist[i]=(char *) malloc(sizeof (char) * numCol[i]);
>     }
>  for(i=0;i<5;i++)
>     {
>       Ipezzo[i]="x=";
>       for (j=0;j<2;j++)
>            labelsHist[i][j]=Ipezzo[i][j];
>     }
>   return 0;
> }
> 
> I have no trouble. If I try to write the method for an object:
> 
> - aggiornaFeedHist
> {
>   int i, j;
>   int numCol[5]={8,8,8,9,10};
>   char *Ipezzo[5];
>   char **labelsHistp;
> 
>   labelsHistp = [[self getZone] alloc: (sizeof (char *) * 5)];
>     for(i=0;i<5;i++)
>       {
>          Ipezzo[i]=[[self getZone] alloc: (sizeof (char) * 2)];
>          labelsHistp[i]=[[self getZone] alloc: (sizeof (char) * numCol[i])];
> /****/   labelsHistp[i]="";
>       }
>   for(i=0;i<5;i++)
>     {
>       Ipezzo[i]="x=";
>       for (j=0;j<2;j++)
>            labelsHistp[i][j]=Ipezzo[i][j]; ***
>     }
> 
>   return self;
> }
> 
> after *** I have segmentation fault.Why? Could somebody help me?

The line marked /****/ above does not appear in your C program. If
it did, then it would crash too. If you remove that line, then
your program won't seg fault, but I venture that it will leak memory
like a digital sieve. If you want to make sure that labelsHistp[i]
is a null string, then replace the marked line with something like
labelsHistp[i][0] = '\0'; or even memset(labelsHistp[i], 0, numCol[i]);
(or if Zone provides a calloc method (it doesn't in 1.4.1) then use
that). To avoid leaking memory, you need to replace the line:

Ipezzo[i]="x=";

with something like

strcpy(Ipezzo[i], "x=");

and when you allocate memory for Ipezzo[i], give it three characters
rather than 2. (The extra character is for the null ('\0') string
terminator.)

Apologies if this is all obvious....

Gary

-- 

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen. AB15 8QH
Tel: +44 (0) 1224 318611               Email: address@hidden

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