The C Programming Language, Ansi C by Brian W Kernighan Dennis M Ritchie

Author:Brian W Kernighan,Dennis M Ritchie [Brian W Kernighan,Dennis M Ritchie]
Language: ita
Format: epub
Published: 2011-10-14T08:27:00+00:00

6.6 Table Lookup

In this section we will write the innards of a table-lookup package, to illustrate more aspects of structures. This code is typical of what might be found in the symbol table management routines of a macro processor or a compiler. For example, consider the #define statement. When a line like #define IN 1

is encountered, the name IN and the replacement text 1 are stored in a table. Later, when the name IN appears in a statement like state = IN;

it must be replaced by 1. There are two routines that manipulate the names and replacement texts. install(s,t) records the name s and the replacement text t in a table; s and t are just character strings. lookup(s) searches for s in the table, and returns a pointer to the place where it was found, or NULL if it wasn't there.

The algorithm is a hash-search - the incoming name is converted into a small non-negative integer, which is then used to index into an array of pointers. An array element points to the beginning of a linked list of blocks describing names that have that hash value. It is NULL if no names have hashed to that value.

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