Wikis / Unreal Wiki / Legacy:Operators

Basics

Preoperators / Postoperators

If any operator is available as pre- and postoperator both versions basically have the same effect on the variable. The only difference is what they return: Preoperators return the variable's new value (after the operator's effect) while postoperators return the old value (the value before the operator did something).

Precedence of operators

The precedence of operators is used to group expressions.

local int a,b,c,d,e;
 
a=2; b=3; c=4; d=2; e=5;
 
                    // log output:
log(a@b@c@d@e);     // 2 3 4 2 5
log(a*b+++c**d*e);  // 86.000000
log(a@b@c@d@e);     // 2 4 4 2 5

UnrealScript actually evaluates the expression like this:

(a * (b++)) + ((c ** d) * e)

You should use a form that uses some spaces and only few (or no) parentheses. This helps understanding the expression a lot when you look at it again after some time:

a * b++ + c**d * e

Boolean Operators

iff (if and only if) 

The word "iff" means "if and only if," implying that if the given condition isn't met, the operation will yield a different (the opposite) result. (This is maths and logic jargon, not an UnrealScript operator.)

short-circuit 

Some binary boolean operators only evaluate their right operand if the result of the entire expression isn't already defined by the result of the first operand. In this case, the right operand is skipped, which is a particularly handy feature if evaluation of that right operand has non-trivial side effects (like a function call) or relies on the left operand's result.

if (bAlreadyConfirmed || ShowMessageBox("Are you sure?")) ...  // show message only when needed

if (ThisPawn != None && ThisPawn.bIsPlayer) ... // prevent "Accessed None"s

Comparison Operators

Comparison operators apply to values of all types. Only compatible types can be compared (numbers with numbers, strings with strings and so on). Object (classes, actors, textures, etc.) and Name properties can only be compared using Equal or Unequal.

Conditional Operator

The conditional operator is a ternary operator in Devastation and UnrealEngine 3 games. In UnrealEngine 3 it has the following syntax:

condition ? expression1 : expression2

In Devastation the syntax is as follows:

condition ?? expression1 : expression2

In both cases it works similar to the If/Else statement, but returns the value of one of the two expressions. If the condition evaluates to True, then the first expression is evaluated, otherwise the second expression is evaluated.

Let's consider an UnrealScript implementation of the global function Max(). In UnrealEngine 1 or 2 you would have to implement it as something like the following:

static final function int Max(int A, int B)
{
  if (A > B) {
    return A;
  }
  else {
    return B;
  }
}

In UnrealEngine 3 you can now express the same feature in a much more compact form:

static final function int Max(int A, int B)
{
  return A > B ? A : B;
}

Very pleasing to the eye and exactly what you mean: Depending on a condition, this function is supposed to return one of two values, not execute one of two statements.

Note that the conditional operator is no general replacement for the If statement! The If statement selects statements to be executed, while the conditional operator selects values to be returned. In fact, you get a compiler error if any of the three operands is a statement that doesn't return a value.

Numeric Operators

Numeric operators apply to values of type int, float and byte.

The modulo operator follows the computer science definition of modulus rather than the mathematical one::

-8 % 10 = -8 (and not 2)

This results from differing interpretations of whether % should be a "modulo" or "remainder" operator (which is not the same thing), as well as differing results of what the integer division operation returns for negative numbers in different programming languages. UnrealScript's definition is consistent with what (most) C/C++ does, which is probably appropriate considering that the language is similar in many other ways. See Useful Maths Functions for the alternative.

The assignment operator = can be combined with +, -, * and /. These combined operators +=, -=, *= and /= assign the result of the operation to the first operand (which must be a variable). These combined assignment operators also return the new value of the variable, so

b += c;      // equivalent to  b = b + c;
a = b += c;  // equivalent to  b = b + c;  a = b;  or  a = (b = b + c);

will add b and c and assign the result to a and b.

Bitwise Operators

For the shift operators, only the 5 least significant bits of the second operand are used.
What does that mean? Well, it's a neat feature that allows you to specify, how many bits you want to stay instead of how many you want to get rid of:

// IntToHex() is a custom function that converts an integer into its hexadecimal string representation
 
// -12 = 0xfffffff4 -> five least significant bits: 0xfffffff4 & 0x0000001f = 0x00000014 = 20
// 12 bits = 3 hex digits; 20 bits = 5 hex digits
 
// shift positive ints                 log output
log(IntToHex(0x02468ace <<   12));  //  68ace000
log(IntToHex(0x02468ace <<  -12));  //  ace00000 = same as 0x02468ace <<  20
log(IntToHex(0x02468ace >>   12));  //  00002468
log(IntToHex(0x02468ace >>  -12));  //  00000024 = same as 0x02468ace >>  20
log(IntToHex(0x02468ace >>>  12));  //  00002468
log(IntToHex(0x02468ace >>> -12));  //  00000024 = same as 0x02468ace >>> 20
 
// shift negative ints (to prove there's no difference from the usual behavior)
log(IntToHex(0xfdb97531 <<   12));  //  97531000
log(IntToHex(0xfdb97531 <<  -12));  //  53100000 = same as 0xfdb97531 <<  20
log(IntToHex(0xfdb97531 >>   12));  //  ffffdb97
log(IntToHex(0xfdb97531 >>  -12));  //  ffffffdb = same as 0xfdb97531 >>  20
log(IntToHex(0xfdb97531 >>>  12));  //  000fdb97
log(IntToHex(0xfdb97531 >>> -12));  //  00000fdb = same as 0xfdb97531 >>> 20

Vector Operators

See also vector.

Here the assignment operator = can also be combined with +, -, * and /. All combined assignment operators have a precedence of 34, so be careful when combining them with the string operators $ and @ since those have a precedence of 40.

Rotator Operators

See also rotator.

Again, the assignment operator = can be combined with +, -, * and /.

Note that rotators can't be inverted with the - preoperator. You will have to use -1 * theRotator- for this operation.

The effect of the rotator/vector operators << and >> can be explained using the result of the global functions GetAxes() and GetUnAxes() function:

static final operator(22) vector << (vector A, rotator B)
{
  local vector X, Y, Z;
  GetAxes(B, X, Y, Z);
  return X * A.X + Y * A.Y + Z * A.Z;
}
 
static final operator(22) vector >> (vector A, rotator B)
{
  local vector X, Y, Z;
  GetUnAxes(B, X, Y, Z);
  return X * A.X + Y * A.Y + Z * A.Z;
}

The << operator performs exactly the calculations required to position a player's weapon in first person view based on a constant view offset vector and the player's view rotation.

String Operators

Aside from the string operators, there are other things that you can do with strings that have been implemented as Global Functions.

Color Operators

Color operators are only available in subclasses of Actor in UnrealEngine 1 and 2. Starting with UnrealEngine 3, they are defined as "global" operators in the Object class.

There are no combined assignment operators for colors.

UnrealEngine 3 also features the "LinearColor" type, which is a color expressed in floating point values. Two operators exist for this type:

Linear colors don't have combined assignment operators either.

Complete Table Of Precedences

The higher an operator is in this table the more tightly it binds.

Related Topics

• UnrealScript main topic page
• Global Function
• Scripting Operators
• Legacy:Operators/Discuss