14.4 Detecting programming errors by linguistic formalism


14.4 Detecting programming errors by linguistic formalism

The front end of a compiler performs lexical, syntactic, and semantic analysis. Not all compilers find the same defects. The more information a compiler has, the more defects it can find. Some compilers operate in a “forgiving” mode but have a “strict” or “pedantic” mode, if you request it.

14.4.1 Regular grammars

Lexical analyzers can find the following errors:

  • Characters in the source that aren’t in the alphabet of the language

  • Words in the source that aren’t in the vocabulary of the language

14.4.2 Context-free grammars

Syntactic analyzers for fixed-form languages such as Fortran and COBOL can find the following errors:

  • Required fields that haven’t been used

  • Incorrect values in a field

  • Invalid continuations of statements across multiple lines

  • Keywords that have been misspelled

  • Required punctuation that is missing

  • Delimiters such as parentheses that are missing

  • Blank or tab characters that are missing

  • Blank or tab characters that shouldn’t occur where they’re found

Syntactic analyzers for free-form languages such as C++ and Java can find the following errors:

  • Comment delimiters that have been put in the wrong place or omitted

  • Literal delimiters that have been put in the wrong place or omitted

  • Keywords that have been misspelled

  • Required punctuation that is missing

  • Construct delimiters such as parentheses or braces that have been misplaced

  • Blank or tab characters that are missing

  • Blank or tab characters that shouldn’t occur where they’re found

14.4.3 Semantic analysis

If a semantic analyzer has a symbol table for each separate procedure, it can find semantic errors that occur because of the following mistakes:

  • Names that aren’t declared

  • Operands of the wrong type for the operator they’re used with

  • Values that have the wrong type for the name to which they’re assigned

If a semantic analyzer has a symbol table for the program as a whole, it can find semantic errors that occur because of the following mistakes:

  • Procedures that are invoked with the wrong number of arguments

  • Procedures that are invoked with the wrong type of arguments

  • Function return values that are the wrong type for the context in which they’re used

If a semantic analyzer has control-flow and data-flow information for each separate procedure, it can find semantic errors that occur because of the following mistakes:

  • Code blocks that are unreachable

  • Code blocks that have no effect

  • Local variables that are used before being initialized or assigned

  • Local variables that are initialized or assigned but not used

If a semantic analyzer has control-flow and data-flow information for the program as a whole, it can find semantic errors that occur because of the following mistakes:

  • Procedures that are never invoked

  • Procedures that have no effect

  • Global variables that are used before being initialized or assigned

  • Global variables that are initialized or assigned, but not used




Debugging by Thinking. A Multidisciplinary Approach
Debugging by Thinking: A Multidisciplinary Approach (HP Technologies)
ISBN: 1555583075
EAN: 2147483647
Year: 2002
Pages: 172

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