🔒 Locked

Returning Arrays

Started by GroZZleR Jan 11, 2003 at 8:54 PM 4 replies 700+ views

Original Post

Jan 11, 2003 at 8:54 PM

Hey all, I''m trying to return an array from a function (or the pointer to the array, same thing more or less). Anyways, the array is declared locally within the function and VC is bitching at me and I can''t help but listen when I get a compiler warning. The warning is saying that I''m returning a temporary or local address. I really need to return 2 values though, from the function, so I can manipulate stuff in another function. Is it okay to return a temporary or local array or is there a better way to return 2 values? Please no STL or anything. Thanks.

Martee

Jan 11, 2003 at 9:03 PM

  
int* returnAnArrayOfInts()
{
   int* foo = new int[2];

   foo[0] = 1;
   foo[1] = 9999;

   return foo;
}

quasar3d

Jan 11, 2003 at 9:10 PM

you can make it a static array

static int array[5];

My Site

Julio

Jan 11, 2003 at 9:12 PM

just a suggestion, but it might be more efficient to pass the array as a parameter of the function.

My Homepage
Freeservers.com sucks. Angelfire.lycos.com is cool.

Nypyren

Jan 11, 2003 at 9:46 PM

if you have a variable that isn't dynamically allocated (no "new" or "malloc"), and is declared inside a funciton, returning it by value will make a copy (if it's an array, you're hosed) to return.

with an array, it would return the pointer to an array that isn't there anymore (exiting the function cleaned up all of the local variabled).

if you say "static" on your variable, they never get cleaned up.

if you say "new" or "malloc" like Martee said, you will be fine, but you would need to delete/free the memory manually later.

If you want to return the values using the parameter list, the parameters need to be a pointer to the type you want to return:

    
void foo(int *int_to_return, char **string_to_return)
{
  *int_to_return = 5;
  char *my_string = new char*[9];
  strcpy(my_string, "testing!");
  *string_to_return = my_string;
}

void main()
{
  int a=0;
  char *str=NULL;

  foo(&a, &str);
  // a is now 5, str is now pointing to that memory with the string.

}

I don't know for sure whether returning an array in the parameter list is faster/slower than returning it via return-value...

return-value can use EAX / parameter doesn't need to set up any additional variable memory (but you have to set it up in the calling function anyway)... If the compiler's smart, it's really fast either way.

[edited by - Nypyren on January 11, 2003 10:50:24 PM]

maknowles7

Jan 15, 2003 at 11:50 AM

To get around the "returning 2 values" issue, if the array you send back is of variable length you can pass in an additional int reference to get the length back:

  
int *returnArray(Foo *doWorkOn, int &arrayLength)
{
    // Do some work with Foo to fill the arrayLength 

    arrayLength = doWorkOn->getArrayLength();

    // create and return array

    int *retArray = new int[arrayLength];

    // fill the array and return it

    return retArray;

}//close returnArray

Another alternative to returning 2 values is to wrap the two values up in a struct or class.
Good luck.
maknowles7

==============================
Matt Knowles
Programmer/Game Developer
www.mak-tech.com
==============================

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.