Implementing a basic jump table for dynamic command parsing

Implementing a basic jump table for dynamic command parsing - Printable Version

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+--- Thread: Implementing a basic jump table for dynamic command parsing (/Thread-Implementing-a-basic-jump-table-for-dynamic-command-parsing)

Implementing a basic jump table for dynamic command parsing - phyrrus9 - 04-17-2018

So, was in a PM with another member who was complaining about having to have a massive command parser with a shitload of if-strncmp's in it. I gave him this C code to solve that problem and be more clean, maybe you guys will like it as well:

Code:
#define ALLOWED_COMMANDS 2

void helpfunc(void)
{
    printf("help message\n");
}
void clearfunc(void)
{
    // some clear function
}

struct jmp_tbl_s
{
    const char *command;
    void (*handler)(void);
} jump_table[ALLOWED_COMMANDS] =
{
    (struct jmp_tbl_s)
    {
        .command = "help",
        .handler = &helpfunc
    },
    (struct jmp_tbl_s)
    {
        .command = "clear",
        .handler = &clearfunc
    }
};

void processCommand(const char *command)
{
    int i;
    size_t cmdlen;
    const size_t len = strlen(command);
    for (i = 0; i < ALLOWED_COMMANDS; ++i)
    {
        cmdlen = strlen(jump_table[i].command);
        if (!strncpy(jump_table[i].command, command, len > cmdlen ? cmdlen : len))
        {
            *(jump_table[i].handler)();
            break;
        }
    }
}

RE: Implementing a basic jump table for dynamic command parsing - drxddock - 04-19-2018

Great code! Easily editable and works great. But what about if the functions needed arguments based on user input?

RE: Implementing a basic jump table for dynamic command parsing - phyrrus9 - 04-19-2018

(04-19-2018, 04:17 PM)0xAeschylus Wrote: Great code! Easily editable and works great. But what about if the functions needed arguments based on user input?

There's 2 ways of attacking that:

Option 1 is to pass the c-string of the command to every function called, and then have a va_list on each of the prototypes, allowing each function to read the rest of the arglist (or parse it ahead of time).
Option 2 is to parse out the arglist based on the command inside that if statement and let every function have a different number of args. To do this, simply remove the void from the proto in the struct, and then C won't enforce the argument list checks and you can pass as many or as few as you need.

I'd advise option 2, then add a "group" field to make it easier