Thread: Is this correct???way of doing??

Hello,

Please anybody here can explain me whether i am doing this correctly or not?i want to create 2 dimesional array of strings with double pointer. Here is the code kindly explain am i doing it fine or is there any mistake in it?

Code:

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

int main(void)
{
char **a,i;
clrscr();

a=(char** )malloc(sizeof(char)*10);

for(i=0;i<10;i++)
{
	a[i]=(char* )malloc(sizeof(char)*4);
	strcpy(a[i],"abc");
	printf("&#37;s\n",a[i]);
}
getch();
return 0;
}

you should not cast malloc in C - see FAQ

your sizeof is wrong - and you have a memory overrun

your indentation also suffers

Code:

a=malloc(sizeof(*a)*10);

Code:

	a[i]=malloc(sizeof(*(a[i])))*4);

I think the first problem is with this line:

Code:

a=(char** )malloc(sizeof(char)*10);

You want an array of 10 strings, but you allocated space for 10 chars. You probably want to use sizeof(char*) instead.

Besides that, I note that we typically include standard headers with angle brackets (<>) instead of double quotes (""). Also, malloc() is declared in <stdlib.h>, but you did not include that... nor did you free() what you malloc()ed, but perhaps it does not really matter for this example.

Note that clrscr() and getch() are non-standard, so you either leave them out and use standard (near) equivalents, or include the relevant non-standard library headers. Oh, and you might want to indent your code better.

You're using an awfully old IDE. Try upgrading.
Here are a few recommendations.

but 1 more question when i dont type cast it by writing (char **) it's giving warning Non-portable Pointer Conversion why does that happen?

Could be due to an old compiler, but I am not sure as C is not my forte.

I suggest testing with:

Code:

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

int main(void)
{
    char **a;
    int i;

    a = malloc(sizeof(char*) * 10);

    for (i = 0; i < 10; i++)
    {
        a[i] = malloc(4);
        strcpy(a[i], "abc");
        printf("&#37;s\n", a[i]);

        free(a[i]);
    }

    free(a);

    return 0;
}

Originally Posted by chottachatri

Ok i got it! thanks

but 1 more question when i dont type cast it by writing (char **) it's giving warning Non-portable Pointer Conversion why does that happen?
i am using Borland Turbo C++ 3.0 IDE

Because Turbo C++ doesn't follow the C89 standard that says that malloc returns a void * and that void * can be cast into anything else.

Or you are using the Turbo C compiler in C++ mode - in which case that's the rules of C++. In that case, change your settings in the IDE so that this file is compiled as C, not C++.

--
Mats

Or get a better IDE.
As for getch, getchar is standard (AFAIK). But there's no easy substitute for clrscr. However, there is an entry in the FAQ for just that, so you can have a look.

Ok and my last question is what are the standard equivalents of clrscr() and getch()?

You could read the cprogramming FAQ or the cpwiki FAQ for the equivalents.