Operators

Operators are built-in symbolic functions — arithmetic, relational, logical, bitwise, assignment — governed by fixed precedence, associativity, and (since C++17) defined evaluation order.

Why it matters

Precedence and evaluation-order surprises cause real bugs: a & b == c parses as a & (b == c) because == binds tighter than &. Short-circuit evaluation of &&/|| is a load-bearing idiom (p && p->ok() guards a null deref). And the three-way <=> operator (C++20) collapses the six comparison operators you used to hand-write into one.

How it works

Each operator has a precedence level and an associativity. A few high-leverage facts:

• && / || short-circuit: the right operand is not evaluated if the left decides the result. There’s a sequence point between them.
• Bitwise (& | ^ ~ << >>) operate per-bit — see bit-manipulation. Lower precedence than comparison, so parenthesize.
• Ternary c ? a : b is the only ternary operator and yields a value.
• <=> (spaceship, C++20) returns an ordering; == != < <= > >= can be auto-generated from it.

Operators	Assoc	Note
::	L→R	tightest
* / %	L→R	above + -
<< >>	L→R	below + -
& ^ |	L→R	below == !=
&& ||	L→R	short-circuits
= += ?:	R→L	loosest

User types add behavior via operator-overloading.

Example

int flags = READ | WRITE;          // OK: | result feeds =
if (flags & WRITE == 0) {}         // BUG: parses as flags & (WRITE==0)
if ((flags & WRITE) == 0) {}       // correct
 
bool ok = ptr && ptr->valid();     // short-circuit guards the deref
auto r = (a <=> b);                // std::strong_ordering in C++20

Pitfalls

• Bitwise vs comparison precedence: always parenthesize (x & MASK) == y.
• Modifying a value twice between sequence points — i = i++ + 1; was UB pre-C++17 and still confusing; avoid.
• Integer division truncates: 5 / 2 == 2; 5 % -3 is implementation-leaning — know your signs.
• << is overloaded for both shifting and stream output (input-output-iostream); std::cout << a << b chains via L→R associativity.

See also

• operator-overloading
• bit-manipulation