staticassert

Staticassert refers to a compile-time assertion mechanism used to verify invariants during compilation rather than at runtime. It is implemented in several languages, most notably in C and C++, and many codebases also provide macro-based emulations for earlier compilers. The primary goal is to catch errors early, such as incorrect type sizes, misaligned data, or invalid template parameters, by forcing a diagnostic failure if a condition is not met.

In C11 and later, the keyword _Static_assert provides a standard mechanism. Syntax: _Static_assert(condition, message); The condition must be a constant expression, and if it evaluates to false, compilation fails with the provided diagnostic message. This form can appear at file scope or within a function body, enabling both global and local invariants to be checked.

Before C11, many C projects used macro-based static assertions as a portability hack. Common patterns include typedef char static_assertion[(condition) ? 1 : -1]; or an enum trick. These techniques rely on the compiler’s handling of array sizes or enum constants to trigger a diagnostic when the condition is false, but they usually yield less informative messages and depend on specific compiler behavior.

In C++, static_assert is a language feature since C++11. Syntax is static_assert(condition, message); where the condition is a constant expression and the message is displayed if the assertion fails. This can be used at namespace scope, class scope, or within templates to enforce compile-time constraints on types and template parameters.

Common uses include validating type sizes, ensuring invariants about template parameters, and guarding against invalid assumptions in generic code. Limitations include portability for pre-C11 C or pre-C++11 compilers and the need for constant expressions. Static assertions remain a widely used tool for early error detection in systems and library code.