An array of function pointers.

[steve]

I'm sorry for clogging the newsgroup with this reply, but my Email keeps
bouncing back.

In article <414 at ucrmath.UUCP>, jantypas at ucrmath.UUCP (John Antypas) writes:
> This may seem like a simple question but I've no luck with an answer so 
> perhaps the net could help.  
> 
> In a graphics application we're writing at work, we have several functions for 
> drawing lines, circles etc.  We'd like to set up something like a vector table.
> If the vector table has a NULL in a spot, then the interpreter will use its
> internal routines instead of faster device specific code.  As an example:
> 
> vectors[] =	{ dev_line(),
> 		  dev_box(),
> 		  dev_circle(),
> 		  dev_arc(),
> 		  dev_text()
> 		}
> 
> This says we have device specific code for all five functions.  Yet when I 
> try to copy function addresses, the compiler complains.  How do I get the
> address of a funciton and put it into an array for calling later?
> 
> Thanks.
> 
> John Antypas -- Soft21 --21st Century Software:
> UUCP: {crash, garp, killer, pyramid, reed, ucsd!ucrmath}!soft21!jantypas
> Internet: jantypas%soft21.uucp@{garp.MIT.EDU, ucsd.EDU}
> Domains:  jantypas@{soft21.Riverside.CA.US, soft21.CTS.COM}

I have some function array code I took from another source a while back.
It works and it shows some of the ways and uses this sort of thing is
usefull for.  Please feel free to use any part of it.  Of course I've
simplified it for you.

--------------------------START OF CODE------------------------------
#define COMMAND_LIST      1
#define COMMAND_ADD       2
#define COMMAND_QUIT      3
#define COMMAND_HELP      4
#define COMMAND_SHOW      5
   
char buffer[150];
char *buffer_place;

struct command_info
    {
    char *name;
    short significant;
    int number;
    void (*function)();
    };

void command_add(),command_help(),command_list(),command_show();

struct command_info command_table[] = {
    { "add",    1,  COMMAND_ADD,   command_add   },
    { "help",   1,  COMMAND_HELP,  command_help  },
    { "list",   1,  COMMAND_LIST,  command_list  },
    { "quit",   1,  COMMAND_QUIT,  NULL          },
    { "show",   1,  COMMAND_SHOW,  command_show  },
    { NULL,     0,  0,             NULL          }};

void run_commands()
    {
    boolean more;
    struct command_info *this_command;
    int linelength;

    more = YES;
    while (more)
        {
        printf("Command : ");
        linelength = readline(stdin,YES);
        if (linelength)
            {
            this_command = get_command(command_table);
            if (this_command->function)
                (*this_command->function)();
            else if (this_command->number == COMMAND_QUIT)
                more = NO;
            else
                {
                printf("Unknown or ambiguious command not understood.\n");
                printf("Type Help for help\n");
                }
            }
        }
    return;
    }

struct command_info *get_command(command_table)
    struct command_info *command_table;

    {
    struct command_info *this_command;
    int count;
    char *this_c;
    boolean more;
    boolean somemore;
    boolean good;

    this_command = command_table;
    more = YES;
    while (this_command->name && more)
        {
        count = 0;
        this_c = this_command->name;
        buffer_place = buffer;
        good = YES;
        somemore = YES;
        while (good && somemore)
            {
            if (*this_c && *buffer_place && *buffer_place != ' ')
                {
                if (*this_c == *buffer_place)
                    {
                    count++;
                    this_c++;
                    buffer_place++;
                    }
                else
                    good = NO;
                }
            else if (*buffer_place && *buffer_place != ' ')
                good = NO;
            else
                somemore = NO;
            }
        if (count >= this_command->significant && good)
            more = NO;
        else
            this_command++;
        }
    return(this_command);
    }
-----------------------------END OF CODE------------------------------


                   enough from this mooncalf - Steven
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These opinions aren't necessarily Motorola's or Remora's - but I'd like to
think we share some common views.
----------------------------------------------------------------------------
Steven R Weintraub                        cs.utexas.edu!oakhill!devsys!steve
Motorola Inc.  Austin, Texas 
(512) 440-3023 (office) (512) 453-6953 (home)
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