> ## 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. # C Bitwise OR Assignment The `|=` operator is the bitwise inclusive OR assignment operator in C. It performs a bitwise OR operation between the binary representations of the left and right operands, and subsequently assigns the computed result to the left operand. ## Syntax and Equivalence ```c theme={"dark"} lvalue |= rvalue; ``` This compound assignment is semantically equivalent to the following expanded form, with the critical distinction that the `lvalue` is evaluated exactly once: ```c theme={"dark"} lvalue = lvalue | (rvalue); ``` The single evaluation is significant when the left operand contains side effects, such as a post-increment operation (e.g., `*ptr++ |= 0x0F;`). ## Mechanics The operator evaluates the operands bit by bit. For each corresponding bit position: * If either or both bits are `1`, the resulting bit is `1`. * If both bits are `0`, the resulting bit is `0`. ```c theme={"dark"} #include int main(void) { uint8_t a = 10; // Binary: 0000 1010 uint8_t b = 6; // Binary: 0000 0110 a |= b; // 'a' becomes 14 // Binary result: 0000 1110 return 0; } ``` ## Type Constraints * **Integral Types Only:** Both operands must be of integral types (e.g., `char`, `short`, `int`, `long`, `unsigned` variants, or `_Bool`). * **Floating-Point Prohibition:** Attempting to use `|=` with floating-point types (`float`, `double`) violates C language constraints and will trigger a compilation error. * **Integer Promotions:** Before the bitwise operation occurs, standard integer promotions are applied to the operands. If the operands have different types, standard arithmetic conversions are performed to bring them to a common type before the OR operation and subsequent assignment.

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