Handling preprocessor-conditioned declarations

Many software systems are developed with configurable functionality, and for multiple hardware platforms and operating systems. This can lead to thousands of possible configurations, requiring each configuration-dependent programming entity or variable to have different types. Such configuration-dependent variables are often declared inside preprocessor conditionals (e.g., C language). Preprocessor-conditioned declarations may be a source of problems. Commonly used configurations are type-checked by repeated compilation. Rarely used configurations are unlikely to be recently type checked, and in such configurations a variable may have a type not compatible to its use or it may contains uses of variables never defined. This paper proposes an approach to identify all possible types each variable declared in a software system can assume, and under which conditions. Inconsistent variable usages can then be detected for all possible configurations. Impacts of preprocessor-conditioned declaration in 17 different open source software systems are also reported.