Malloc question

[asm2hex]

Hello,

I have a quick question I want to ask. How can I copy the data from a allocated variable, so that when I free up the allocated variable the copied data isn't erased with it.

Thanks,
-A2H

[Gonbe]

I'm not sure if I understand your question correctly, but you could just copy the data like you would with non-allocated data. So something like this is what I mean:

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

#define AMOUNT_OF_DATA 20

int main (int argc, char *argv[])
{
    int *allocatedData = (int*) malloc(AMOUNT_OF_DATA * sizeof(int));
    int i = 0;

    //putting data in the allocated memory:
    for (i = 0; i < AMOUNT_OF_DATA; i++)
        allocatedData[i] = i + 1;

    printf("Contents of allocatedData:\n");
    for (i = 0; i < AMOUNT_OF_DATA; i++)
        printf("%d ", allocatedData[i]);

    //Make a copy
    int dataCopy[AMOUNT_OF_DATA];

    //Copy the data from the allocated memory to the new variable.
    for (i = 0; i < AMOUNT_OF_DATA; i++)
        dataCopy[i] = allocatedData[i];

    //Freeing the allocated memory
    free(allocatedData);

    //Showing contents of the copy
    printf("\n\nContents of dataCopy:\n");
    for (i = 0; i < AMOUNT_OF_DATA; i++)
        printf("%d ", dataCopy[i]);

    return 0;
}

Will result in the following output:

Contents of allocatedData:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Contents of dataCopy:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

[asm2hex]

Yes that's exactly what I'm talking about. How ever, when I free the allocated data. The newly copied data is erase as well.

[asm2hex]

Maybe this will give a clearer meaning of what I'm trying to do.

struct{
	char *info[256];
	int ipid;
}CopyAllc;
...
char *token[256];
char *FBUFFER;
		FBUFFER = malloc(sizeof(char)*lSize);
		if(FBUFFER == NULL){ 
			DisplayError("Memory Allocation Error!");
			return 0;
		}
		fread(FBUFFER, sizeof(lSize), lSize, infoFile);  
		fclose(infoFile);
	
		token[i] = strtok(FBUFFER, "\n\r ");
		while(token[i] != NULL){					     
			++i;
			token[i] = strtok(NULL, "\n\r ");
		}
		for(i = 0; i < sizeof(token); i++){
                       if(token[i] == NULL) break;
			CopyAllc.info[i] = token[i];
		}
free(FBUFFER); //erases the copied data from CopyAllc.info as well.

[Narue]

>Maybe this will give a clearer meaning of what I'm trying to do.
strtok doesn't make a copy of the token, it modifies the original string by adding a null character at the end of each token and then returns a pointer to it. Every pointer in token, and consequently every pointer in CopyAllc.info, is actually a pointer to your dynamically allocated memory. When the memory goes away, so do all references to it.

You need to make the copy yourself:

// Was CopyAllc.info[i] = token[i];
{
  CoypAllc.info[i] = malloc ( strlen ( token[i] ) + 1 );

  if ( CopyAllc[i] == NULL ) {
    /* Handle the error */
  }

  strcpy ( CopyAllc[i], token[i] );
}

Now for some general commments.

>FBUFFER = malloc(sizeof(char)*lSize);
sizeof(char) is guaranteed to evaluate to 1, so you can simplify your call to malloc:

FBUFFER = malloc ( lSize );

Also, an unadorned size is suspicious when allocating memory for a string. Usually I'd expect +1 for the null character:

FBUFFER = malloc ( lSize + 1 );

>for(i = 0; i < sizeof(token); i++){
There are two things I'd recommend on this:

1. sizeof(token) is not sufficient to get the size of an array unless it's an array of char. You need sizeof token / sizeof *token because token is an array of pointers to char. sizeof gives you the total bytes in the array, and dividing it by the size of a single element gives you the number of elements.
2. You're wasting time processing NULL elements. Instead of walking across the whole array, you can use the current value of i (rather than resetting it to 1) as the limit:

   while ( i >= 0 ) { /* Assuming i is an int */
     /* Copy token[i] to CopyAllc.info[i] */
   
     --i;
   }

   In this case the order is irrelevant. You can copy from back to the front without altering the result.