post/preincrementing function arguments

[silk.odyssey]

I have a recursive function that accepts an integer value. Everytime the function is called the value passed is incremented. If I use the postincrement operator the value is not incremented but if I use preincrement it is. Why is this?

[Codeplug]

Let me be the first the make a wild guess as to what the code looks like:

foo(i++); vs foo(++i);

The first one increments i then calls foo(i), the second one calls foo(i) then increments i.

gg

[Prelude]

>Everytime the function is called the value passed is incremented.
Save yourself problems like this and don't actually change the value, just pass it added by one:

recursive_func ( val + 1 );

This is even more important when you do something using val after the recursive call. If you didn't really want it incremented then you'll have issues:

#include <iostream>

using namespace std;

// Uncomment for correct operation and compare
//#define CORRECT

void tabme ( int val )
{
  if ( val == 6 )
    return;
  for ( int i = 0; i < val; i++ )
    cout<<'\t';
  cout<<"In: "<< val <<'\n';
#ifdef CORRECT
  tabme ( val + 1 );
#else
  tabme ( ++val );
#endif
  for ( int i = 0; i < val; i++ )
    cout<<'\t';
  cout<<"Out: "<< val <<'\n';
}

int main()
{
  tabme ( 0 );
}

[silk.odyssey]

i am not sure I understand why val + 1 produces a different result than ++val.

[anonytmouse]

http://www.embedded.com/story/OEG20020429S0037
http://www.embedded.com/showArticle....icleID=9900661

EDIT:

Ignore this post. There is nothing undefined about either of:

foo(i++);
foo(++i);

which is lucky, since we use both constructs frequently.

Technically, it turns out that in both constructs i is incremented before the function call. However, i++ returns the value of i before it is incremented while ++i returns the value of i after it is incremented.

It turns out there is a sequence point:

foo(sequence_point_here);

which means that all arguments and side effects must happen before the function call.

However, when two or more arguments are involved, there is no rule about order of evaluation.

[Prelude]

>i am not sure I understand why val + 1 produces a different result than ++val
Because ++val changes val, val + 1 does not.