In computer science, a dispatch table is a list of pointers to the actual implementation of each method (computer science). Use of such a table is a common technique when implementing late binding in object-oriented programming. Generally, OOP languages support the table as a built-in feature to provide seamless late binding.

=Hand-coded implementation=

Example implementation in C programming language (Spinellis, 2003, pp. 312–313). The following structure declaration—excerpted from the FreeBSD/NetBSD implementation of the pax archive reading and writing program—contains pointers to functions used for performing archive processing operations:

typedef struct { char *name; /* name of format, this is the name the user */ /* [...] */ int (*id)(char *, int); /* checks if a buffer is a valid header */ int (*st_rd)(void); /* initialize routine for read. */ int (*rd)(ARCHD *, char *);/* read header routine. */ off_t (*end_rd)(void); /* read cleanup. */ int (*st_wr)(void); /* initialize routine for write operations */ int (*wr)(ARCHD *); /* write archive header. */ int (*end_wr)(void); /* end write. write the trailer and do any */ int (*trail)(char *, int, int *); /* returns 0 if a valid trailer, -1 if not */ int (*subtrail)(ARCHD *); /* read/process file data from the archive */ int (*rd_data)(ARCHD *, int, off_t *); /* read/process file data from the archive */ int (*wr_data)(ARCHD *, int, off_t *); /* write/process file data to the archive */ int (*options)(void); /* process format specific options (-o) */ } FSUB;

An array of these structures is initialized with functions appropriate for each different archive type:

FSUB fsub[] = { /* 0: OLD BINARY CPIO */ { bcpio , bcpio_id, cpio_strd, bcpio_rd, bcpio_endrd, cpio_stwr, bcpio_wr, cpio_endwr, NULL, cpio_subtrail, rd_wrfile, wr_rdfile, bad_opt },

/* 1: OLD OCTAL CHARACTER CPIO */ { cpio , cpio_id, cpio_strd, cpio_rd, cpio_endrd, cpio_stwr, cpio_wr, cpio_endwr, NULL, cpio_subtrail, rd_wrfile, wr_rdfile, bad_opt },

/* 2: SVR4 HEX CPIO */ { sv4cpio , vcpio_id, cpio_strd, vcpio_rd, vcpio_endrd, cpio_stwr, vcpio_wr, cpio_endwr, NULL, cpio_subtrail, rd_wrfile, wr_rdfile, bad_opt },

/* 3: SVR4 HEX CPIO WITH CRC */ { sv4crc , crc_id, crc_strd, vcpio_rd, vcpio_endrd, crc_stwr, vcpio_wr, cpio_endwr, NULL, cpio_subtrail, rd_wrfile, wr_rdfile, bad_opt },

/* 4: OLD TAR */ { tar , tar_id, no_op, tar_rd, tar_endrd, no_op, tar_wr, tar_endwr, tar_trail, NULL, rd_wrfile, wr_rdfile, tar_opt },

/* 5: POSIX USTAR */ { ustar , ustar_id, ustar_strd, ustar_rd, tar_endrd, ustar_stwr, ustar_wr, tar_endwr, tar_trail, NULL, rd_wrfile, wr_rdfile, bad_opt } };

At runtime, all operations are performed through a FSUB pointer—frmt in the following example—thus dispatching control to the appropriate method for the archive being processed:

/* * pass the format any options and start up format */ if return;

=OOP compiler implementation=

In object-oriented programming languages the compiler will automatically create a dispatch table for objects with dynamically bound methods. This table is called a virtual table or vtable.

=References=