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3.5.1 Data Type of Locations

Defining a data type for locations is much simpler than for semantic values, since all tokens and groupings always use the same type.

You can specify the type of locations by defining a macro called YYLTYPE, just as you can specify the semantic value type by defining a YYSTYPE macro (see section Data Types of Semantic Values). When YYLTYPE is not defined, Bison uses a default structure type with four members:

typedef struct YYLTYPE
  int first_line;
  int first_column;
  int last_line;
  int last_column;

While default locations represent a range in the source file(s), this is not a requirement. It could be a single point or just a line number, or even more complex structures.

When YYLTYPE is not defined, at the beginning of the parsing, Bison initializes all these fields to 1 for yylloc. To initialize yylloc with a custom location type (or to chose a different initialization), use the %initial-action directive. See section Performing Actions before Parsing.