What does it mean when the first “for” parameter is blank?

Question

I have been looking through some code and I have seen several examples where the first element of a for cycle is omitted.

An example:

for ( ; hole*2          


        

Answer 1

It just means that the user chose not to set a variable to their own starting value.

for(int i = 0; i < x; i++)

is equivalent to...

int i = 0;
for( ; i < x; i++)

EDIT (in response to comments): These aren't exactly equivalent. the scope of the variable i is different.

Sometimes the latter is used to break up the code. You can also drop out the third statement if your indexing variable is modified within the for loop itself...

int i = 0;
for(; i < x;)
{
...
i++
...
}

And if you drop out the second statement then you have an infinite loop.

for(;;)
{
runs indefinitely
}

Answer 2

It means that the initial value of hole was set before we got to the loop.

Looks like a list traversal of some kind.