Source-to-Source Refactoring and Elimination of Global Variables in C Programs

A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author’s publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.A global variable in C/C++ is one that is declared outside a function, and whose scope extends the lifetime of the entire program. Global variables cause problems for program dependability, maintainability, extensibility, verification, and thread-safety. However, global variables can also make co ding more convenient and improve program performance. We have found the use of global variables to remain unabated and extensive in real-world software. In this paper we present a source-to-source refactoring tool to au tomatically detect and localize global variables in a program. We implement a compiler based transformation to find the best location to redefine each global va riable as a local. For each global, our algorithm initializes the corresponding new local variable, pa sses it as an argument to necessary functions, and updates the source lines that used the global to now instead use th e corresponding local or argumen t. We also characterize the use of global variables in standard benchmark programs. We study the effect of our transformation on static program properties, such as change in the number of function ar guments and program state visibility. Additionally, we quantify dynamic program features, including memory and runtime performance, before and after our localizing transformation