What is the "-->" operator in C/C++?
After reading Hidden Features and Dark Corners of C++/STL on comp.lang.c++.moderated
, I was completely surprised that the following snippet compiled and worked in both Visual Studio 2008 and G++ 4.4.
Here's the code:
#include <stdio.h>
int main()
{
int x = 10;
while (x --> 0) // x goes to 0
{
printf("%d ", x);
}
}
Output:
9 8 7 6 5 4 3 2 1 0
I'd assume this is C, since it works in GCC as well. Where is this defined in the standard, and where has it come from?
Solution 1:
-->
is not an operator. It is in fact two separate operators, --
and >
.
The conditional's code decrements x
, while returning x
's original (not decremented) value, and then compares the original value with 0
using the >
operator.
To better understand, the statement could be written as follows:
while( (x--) > 0 )
Solution 2:
Or for something completely different... x
slides to 0
.
while (x --\
\
\
\
> 0)
printf("%d ", x);
Not so mathematical, but... every picture paints a thousand words...
Solution 3:
That's a very complicated operator, so even ISO/IEC JTC1 (Joint Technical Committee 1) placed its description in two different parts of the C++ Standard.
Joking aside, they are two different operators: --
and >
described respectively in §5.2.6/2 and §5.9 of the C++03 Standard.