conditional_stack_empty.md

conditional_stack_empty

Location

src/fe_utils/conditional.c:130-139

Overview

Determines whether the conditional stack is empty, indicating that there are no active \if-blocks currently being processed.

Definition

bool conditional_stack_empty(ConditionalStack cstack)

Detailed Description

This function provides a simple boolean test to determine if the conditional stack contains any elements. It checks whether the head pointer of the stack is NULL, which indicates an empty stack with no active conditional blocks. This is a fundamental utility function used extensively throughout PostgreSQL frontend tools to determine when conditional processing is inactive, which affects how commands should be executed and whether certain conditional commands (like \elif, \else, \endif) are valid.

Parameters / Member Variables

• cstack: A ConditionalStack pointer representing the conditional stack to check. The function directly accesses the head field to determine emptiness.

Dependencies

• Functions called/Symbols referenced:
  • ConditionalStack (typedef)
• Called from (representative examples):
  • advanceConnectionState (pgbench) - multiple locations
  • executeMetaCommand (pgbench)
  • CheckConditional (pgbench) - multiple locations
  • MainLoop (psql) - multiple locations
  • conditional_stack_peek (conditional utility)
  • conditional_stack_poke (conditional utility)
  • conditional_stack_set_query_len (conditional utility)
  • conditional_stack_get_query_len (conditional utility)
  • conditional_stack_set_paren_depth (conditional utility)
  • conditional_stack_get_paren_depth (conditional utility)

Notes and Other Information

• Simple and efficient O(1) operation that just checks the head pointer
• Critical for determining when conditional commands are valid or invalid
• Used as a guard condition in many other conditional stack operations
• The function assumes the cstack parameter is not NULL - calling with NULL would cause undefined behavior
• Widely used across PostgreSQL frontend utilities for conditional command processing logic

Simplified Source

bool conditional_stack_empty(ConditionalStack cstack) {
    // Simply check if head pointer is NULL
    return cstack->head == NULL;
}