14 .TH sym 3 "8 May 1999" mLib
16 sym \- symbol table manager
28 .B "#include <mLib/sym.h>"
30 .BI "void sym_create(sym_table *" t );
31 .BI "void sym_destroy(sym_table *" t );
33 .BI "char *SYM_NAME(void *" p );
34 .BI "void *sym_find(sym_table *" t ,
35 .BI " const char *" n ", long " l ,
36 .BI " size_t " sz ", unsigned *" f );
37 .BI "void sym_remove(sym_table *" t ", void *" b );
39 .BI "void sym_mkiter(sym_iter *" i ", sym_table *" t );
40 .BI "void *sym_next(sym_iter *" i );
45 functions implement a data structure often described as a dictionary, a
46 finite map, an associative array, or a symbol table. It associates
50 such that the value corresponding to a given key can be found quickly.
51 Additionally, all stored associations can be enumerated.
53 The interface provides an
55 symbol table. The data objects stored in the table must include a small
56 header used by the symbol table manager. This reduces the amount of
57 pointer fiddling that needs to be done, and in practice doesn't seem to
58 be much of a problem. It's also fairly easy to construct a
59 non-intrusive interface if you really want one.
61 There are three main data structures involved in the interface:
64 Keeps track of the information associated with a particular table.
67 The header which must be attached to the front of all the value
71 An iterator object, used for enumerating all of the associations stored
74 All of the above data structures should be considered
76 don't try looking inside. Representations have changed in the past, and
77 they may change again in the future.
78 .SH "CREATION AND DESTRUCTION"
81 object itself needs to be allocated by the caller. It is initialized by
82 passing it to the function
84 After initialization, the table contains no entries.
86 Initializing a symbol table involves allocating some memory. If this
91 When a symbol table is no longer needed, the memory occupied by the
92 values and other maintenance structures can be reclaimed by calling
94 Any bits of user data attached to the symbol table values should have
95 previously been destroyed.
96 .SH "ADDING, SEARCHING AND REMOVING"
97 Most of the actual work is done by the function
99 It does both lookup and creation, depending on its arguments. To do its
100 job, it needs to know the following bits of information:
103 A pointer to a symbol table to manipulate.
108 to look up or create. Usually this will be a simple text string,
109 although it can actually be any arbitrary binary data.
112 The length of the key. If this is \-1,
114 assumes that the key is a null-terminated string, and calculates its
118 The size of the value block to allocate if the key could not be found.
119 If this is zero, no value is allocated, and a null pointer is returned
120 to indicate an unsuccessful lookup.
123 The address of a `found' flag to set. This is an output parameter. On
126 will set the value of
128 to zero if the key could not be found, or nonzero if it was found. This
129 can be used to tell whether the value returned has been newly allocated,
130 or whether it was already in the table.
134 will return the key associated with a given value block. You must use
135 this macro rather than fiddling inside the
139 A symbol can be removed from the table by calling
141 passing the symbol table itself, and the value block that needs
144 Enumerating the values in a symbol table is fairly simple. Allocate a
146 object from somewhere. Attach it to a symbol table by calling
148 and passing in the addresses of the iterator and the symbol table.
151 will return a different value from the symbol table, until all of them
152 have been enumerated, at which point,
154 returns a null pointer.
156 It's safe to remove the symbol you've just been returned by
158 However, it's not safe to remove any other symbol. So don't do that.
160 When you've finished with an iterator, it's safe to just throw it away.
161 You don't need to call any functions beforehand.
162 .SH "USE IN PRACTICE"
163 In normal use, the keys are simple strings (usually identifiers from
164 some language), and the values are nontrivial structures providing
165 information about types and values.
167 In this case, you'd define something like the following structure for
171 sym_base _base; /* Symbol header */
172 unsigned type; /* Type of this symbol */
173 int dispoff; /* Which display variable is in */
174 size_t frameoff; /* Offset of variable in frame */
181 you can find the variable's name by calling
182 .BI SYM_NAME( v )\fR.
184 You can look up a name in the table by saying something like:
186 val *v = sym_find(t, name, -1, 0, 0);
188 error("unknown variable `%s'", name);
190 You can add in a new variable by saying something like
193 val *v = sym_find(t, name, -1, sizeof(val), &f);
195 error("variable `%s' already exists", name);
198 You can examine all the variables in your symbol table by saying
204 for (sym_mkiter(&i, t); (v = sym_next(&i)) != 0; ) {
208 That ought to be enough examples to be getting on with.
210 The symbol table manager requires the suballocator (see
212 for details). You must ensure that
214 has been called before using any symbol tables in your program.
216 The symbol table is an extensible hashtable, using a 32-bit CRC as the
217 hash function. The hash chains are kept very short (probably too short,
218 actually). Every time a symbol is found, its block is promoted to the
219 front of its bin chain so it gets found faster next time.
224 Mark Wooding, <mdw@nsict.org>