Analyzing Symbol Table Statements in Compiler Design

The question asks us to identify the statement about a symbol table that is false. A symbol table is a crucial data structure used by a compiler to store information about identifiers (like variables, functions, etc.) encountered in the source code. Let's analyze each statement:

Statement Analysis

Statement 1: Symbol table tracks variable scope.

This statement is true. A key role of the symbol table is to manage the scope of variables. It records where each variable is declared and accessible (e.g., globally, within a specific function, or inside a block). This helps the compiler ensure that variables are used according to the rules of their scope and prevents issues like using undeclared variables or accessing variables outside their valid region.

Statement 2: Symbol table implementation using BST.

This statement is true. Various data structures can implement a symbol table. A binary search tree (BST) is one such possibility, offering efficient ways to insert, search, and delete entries. Other common implementations include hash tables and arrays. The choice often depends on the specific requirements for performance and the expected number of entries.

Statement 3: Symbol table not required after parsing phase.

This statement is false. The symbol table is essential throughout multiple phases of the compilation process, not just up to the parsing phase. While parsing builds and initially populates the table, subsequent phases like semantic analysis (where type checking and scope resolution are verified), intermediate code generation, and optimization rely heavily on the information stored in the symbol table. For example, semantic analysis needs the table to check if variable types match their usage and if scopes are correctly handled.

Statement 4: Symbol table creation during lexical analysis.

This statement is true. The process of building the symbol table often begins during the lexical analysis phase. As the lexical analyzer (scanner) reads the source code and groups characters into tokens (like identifiers, keywords, operators), it encounters identifiers. These identifiers are typically entered into the symbol table during this early stage.

Conclusion

Based on the analysis, the statement that is false is that the symbol table is not required after the parsing phase. It continues to be vital for semantic analysis and code generation.