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Expression evaluation

Describes implementation-defined aspects of the ARM C compiler and C library relating to expression evaluation, as required by the ISO C standard.

The compiler can re-order expressions involving only associative and commutative operators of equal precedence, even in the presence of parentheses. For example, a + (b + c) might be evaluated as (a + b) + c if a, b, and c are integer expressions.

Between sequence points, the compiler can evaluate expressions in any order, regardless of parentheses. Therefore, side effects of expressions between sequence points can occur in any order.

The compiler can evaluate function arguments in any order.

Any aspect of evaluation order not prescribed by the relevant standard can be varied by:

  • The optimization level you are compiling at.

  • The release of the compiler you are using.