simple char** practice

im just wondering if im using a 'char**' (and dynamic memory) properly, if you could let me know. ie, missing another set of []'s or a * or & somewhere.

Code:

---

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

int main()
{
   
    char* test= "hello there";
   
    char** temp = (char**) malloc(sizeof(char**) * 1);

    temp[0] = (char*) malloc(sizeof(char*)* 20);
   
    strcpy(temp[0],test);
    printf("'&#37;s'\n",temp[0]);
   
    free(temp[0]);
    free(temp);
   
    getchar();
}

---

i know this program isnt useful, im just wondering if it is correct.
thanks

Aside from all the pointless allocation typecasts, you're not quite there.

Code:

---

char **ptp;

size_t num = 1; /* Purely for illustration purposes. */

ptp = malloc( num * sizeof *ptp ); /* Allocate one pointer to a character. */
if( ptp )
    ptp[0] = malloc( /* number of characters to allocate */ );
...
free( ptp[0] ); /* Free allocated characters. */
free( ptp ); /* Free the pointer to a character. */

---

Quzah.

Code:

---

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

int main()
{
   
    char* test= "hello there";
   
    char** temp = (char**) malloc(sizeof(char*) * 1);

    temp[0] = (char*) malloc(sizeof(char)* 20);
   
    strcpy(temp[0],test);
    printf("'&#37;s'\n",temp[0]);
   
    free(temp[0]);
    free(temp);
   
    getchar();
}

---

I believe you're allocating the wrong amount of memory, however, since char * and char ** are the same in your case, you shouldn't experience any problems for the first allocation. The second allocation is very different. You were allocating 4 times as much memory by allocating 20 char *'s when you should have been allocating 20 chars.

Take care to understand what you are malloc()ing. This is why the FAQ on malloc() refers to using a format similar to this:

Code:

---

int *p;
...
p = malloc(sizeof(*p));

---

If you're using a C89 compiler, you probably casted malloc() to make the compiler shut up about the error, when the reason for the error was that you forgot to include stdlib.h. On a C99 compiler, you can't get away with that.

thanks for the response.

edit: @Quzah:
im not sure what you mean though.. ie, what did i miss that i 'wasnt there'? (aside from the checking if malloc failed to allocate the memory, which i just overlooked and assumed it worked in my example)

edit2: i think you were illustrating something that MacGyver said right? (i didnt pay close enough attention to it!)

edit3: @MacGyver:
Thanks alot for the info :) im using DevC++ and didnt get any warnings.. im sure i would have if i was on my linux boot with gcc.

appreciated folks

Quote:

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Originally Posted by nadroj

edit2: i think you were illustrating something that MacGyver said right?

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Considering that he posted after I did, no I wasn't illustrating his post.

Quote:

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Originally Posted by nadro

(i didnt pay close enough attention to it!)

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Then what's the point of asking a question here?


Quzah.

i didnt mean you 'copied' off of him or something childish like that because i know you posted before him.

and i simply overlooked the difference in your code.