Skip to main content

Documentation Index

Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt

Use this file to discover all available pages before exploring further.

The | operator in C++ is the bitwise inclusive OR operator. It performs a logical disjunction on each corresponding pair of bits from two integral operands, yielding a new value where a bit is set to 1 if at least one of the corresponding bits in the operands is 1, and 0 otherwise.

​
Syntax

result = expression1 | expression2;

​
Bitwise Truth Table

The operator evaluates the operands at the binary level according to the following truth table: | Bit 1 (expression1) | Bit 2 (expression2) | Result (|) | | :---: | :---: | :---: | | 0 | 0 | 0 | | 0 | 1 | 1 | | 1 | 0 | 1 | | 1 | 1 | 1 |

​
Type Requirements and Promotions

  • Valid Types: The built-in | operator requires both operands to be of integral types (e.g., int, char, long, unsigned) or unscoped enumeration types.
  • Integer Promotion: Before the operation is performed, C++ applies standard integer promotions. Operands smaller than int (like char or short) are promoted to int (or unsigned int).
  • Usual Arithmetic Conversions: If the operands are of different types after promotion, the compiler applies usual arithmetic conversions to bring them to a common type, which also dictates the type of the evaluated result.

​
Compound Assignment

C++ provides a compound assignment operator, |=, which applies the bitwise OR operation and assigns the result directly to the left operand. 
expression1 |= expression2;
While logically similar to the expanded form expression1 = expression1 | expression2;, there is a critical semantic difference regarding expression evaluation. In the compound assignment (|=), expression1 is evaluated exactly once. In the expanded form, expression1 is evaluated twice. This distinction is vital if expression1 contains side effects. For example, arr[i++] |= 5; evaluates the index and increments i only once, whereas arr[i++] = arr[i++] | 5; evaluates the side effect twice.

​
Evaluation Semantics

Unlike the logical OR operator (||), the bitwise OR operator (|) does not short-circuit. Both expression1 and expression2 are fully evaluated before the bitwise operation occurs, regardless of the value of the first operand. Furthermore, the evaluation order of the operands for the built-in | operator remains unsequenced across all C++ standards (including C++17 and later). The compiler is free to evaluate expression1 before expression2, or vice versa.

​
Operator Overloading

For user-defined types (classes, structs, or scoped enumerations), the | operator can be overloaded. When overloaded, it loses its strict bitwise semantics unless explicitly implemented to mimic them. 
// Example signature for a non-member overloaded | operator
ReturnType operator|(const CustomType& lhs, const CustomType& rhs);
Master C++ with Deep Grasping Methodology!Learn More