Abstract: Definition and reference are two kinds of operations that software variable.The operation that software variable disobeys the variable using rules will result in software error.In order to detect these kinds of software error,the definition-reach data-flow analysis and living-variable data-flow analysis of a program must be made.There may be more than one path to a program’s site,and the data-flow states on one program path may be different from the others.So the must-data-flow and the may-data-flow of a program were calculated to depict the accurate data-flow information.The control structure on basic block is used by the data-flow analysis method.The factors that will affect the data-flow such as definition information that can reach to a basic block entry site and exit site,living variable that can reach to a basic block,some special operation such as memory allocate operation and memory free operation,and the relations between them were discussed sufficiently.

Key words: Software error,Software error detection,Data-flow analysis