function returning pointer

Code:

---

#include<stdio.h>
int* func(int x);
int c[5]={9,6,7,8};
int main()
{
int a[5]={1,2,3,4};
int *p;
p = func(a[0]);
printf("%d",p[1]);
}

int* func(int x)
{
 int* b = new int[5];
 if((x==c[0]||x==c[1]))
 {b[0]=10;}
  else
 {
 b[0]=25;
 b[1]=20;
 b[2]=69;
 }
 return b;
 delete b;  //  can i place delete here ?
}

---

question
------------

this code is working. but how do i know how many elements are actually returned by the ponter b ?

in fact here 3 elements(i.e b[0],b[1],b[2]) are returned in the above code.

how does the caller know how many is returned so that he could print all the returned elements.

>this code is working.
My compiler disagrees.

>how does the caller know how many is returned so that he could print all the returned elements.
Use an extra pointer argument to the function that saves the number of elements.

>delete b; // can i place delete here ?
Not in C.

>>how does the caller know
It doesn't

>>int* b = new int[5];
Please don't post C++ on the C forum. There's a C++ forum over here

>> return b;
>>delete b;
The delete will never run, which is actually a good thing as you've just returned the pointer to the caller for their use.

Try something like this:

Code:

---

#include <stdio.h>
 #include <stdlib.h>
 
 int foo(int **i)
 {
  *i = malloc(sizeof(**i) * 10);
 
  if (*i)
    return (10);
  else
    return 0;
 }
 
 int main(void)
 {
  int *p;
  int i;
 
  i = foo(&p);
 
  if (i)
  {
    printf ("Space for %d ints malloc'ed\n", i);
    free (p);
  }
 
  return(0);
 }

---

>My compiler disagrees

i am using g++...it works. i printed p[0],p[1] ,..its giving result 25,20 respectively.


>Use an extra pointer argument to the function that saves the number of elements.

do u suggest to return a structure ?

is there no easy way?


sorry Hammer...for using new , delete in C code. i dislike malloc. new delete are compact and comfortable.

anyway assume that is a C code only. i wanted to print all the returned elements in my code.

something like below.....

for(int m=0;m<no_of_returned_elements;m++)
printf("%d",p[m]);


how can achieve my goal ?

>i am using g++...it works.
I'm compiling as C...it most certainly doesn't work.

>how can achieve my goal ?
This is what I meant:

Code:

---

#include<stdio.h>
#include<stdlib.h>
int* func(int x, int *n);
int c[5]={9,6,7,8};
int main()
{
  int a[5]={1,2,3,4};
  int *p;
  int m, n;
  p = func(a[0],&n);
  for(m=0;m<n;m++)
    printf("%d ",p[m]);
}

int* func(int x, int *n)
{
  int* b = malloc(5 * sizeof *b);
  if((x==c[0]||x==c[1]))
  {
    b[0]=10;
    *n = 1;
  }
  else
  {
    b[0]=25;
    b[1]=20;
    b[2]=69;
    *n = 3;
  }
  return b;
}

---

But a structure will work too.

The number of elements used could either be passed as a parameter to the function (in the form of a pointer, of course), or you could use a sentinel value to mark the end of the array (just as strings are zero-terminated).

>> return b;
>> delete b;

Anything that appears after a return statement will not get executed. Second, you shouldn't delete the memory from within the function since it is being used afterward! Instead, either return the dynamic memory to the caller, and let the caller clean it up later (not recommended), or just create the array from the callers scope and pass it as a parameter to the function.

Another thing I noticed was that the function references a global variable. This is almost always a very bad idea. A much better way would be to pass the variable as a parameter.

Code:

---


#include<stdio.h>

int * func(
 int param,
 int dest[],
 int src[],
 int max_elements,
 int * used);

int c[5]={9,6,7,8};

int main()
{
 int a[5]={1,2,3,4};
 int b[5];
 int *p;
 int total;

 p = func(a[0], b, c, 5, &total);

 printf("%d",p[1]);

 return 0;
}

int * func(
 int param,
 int dest[],
 int src[],
 int max_elements,
 int * used)
{
  *used = 0;

        if((param==src[0]||param==src[1]))
        {
            if(max_elements >= 1)
          {
            dest[0]=10;
            *used = 1;
          }
        }
        else
      {
            if(max_elements >= 3)
          {
            dest[0]=25;
            dest[1]=20;
            dest[2]=69;
            *used = 3;
          }
      }

 return dest;
}

---

very smart solution indeed. i did not want to use structure. i was thinking some other good method. i liked your solution . its allright.

Quote:

---

you could use a sentinel value to mark the end of the array


you shouldn't delete the memory from within the function since it is being used afterward!


Another thing I noticed was that the function references a global variable. This is almost always a very bad idea. A much better way would be to pass the variable as a parameter

---

your coments are very much informative to me. thanks...i will try to use later.