Table lookup for functions..

**Samuel Maciel** · 09-16-2012

hey guys im trying to make a table look up for a collection of functions so i have chosen to use a table look up with a function pointer run by a 2 character string..

Code:

const struct Node{
    char cmd[3];                   // type this letter
    void (*fnctPt)(void);};        // to execute this command


typedef const struct Node NodeType;
typedef NodeType * NodePtr;

NodeType TL[]={ // linear linked list
{ "FF", &Forward},
{ "RR", &Reverse},
{ "TL", &Turn_L},
{ "TR", &Turn_R},
{ "RL", &Rotate_L},
{ "RR", &Rotate_R},
{ "HH", &Cmd_OPT}};


void Interpreter(char *string){
    NodePtr pt;
    const int table_length = sizeof(TL)/sizeof(*TL);
    int row;


    for(row=0; row < table_length; row++){
        pt = &TL[row];
        if(strcmp(string, &pt->cmd)){
            pt->fnctPt();
        }
        else{
            SCI_OutString("Error");
        }
    }
}

if any of youhave time to try it here is the current project
https://www.dropbox.com/s/s9lcvzlmax3e8it/proj.zip

**oogabooga** · 09-16-2012

I don't understand this comment:

Code:

NodeType TL[]={ // linear linked list

"Linked" implies pointers to connect the elements.

You don't need the ampersands in front of the function names.

This

Code:

if(strcmp(string, &pt->cmd)){

should be

Code:

if(strcmp(string, pt->cmd) == 0){

And you should break out of the loop when a match is found.

And the error output should happen AFTER the loop, not inside it:

Code:

    if (row == table_length)
        SCI_OutString("Error");

Other than that, you didn't really ask a question, so ....

**Samuel Maciel** · 09-16-2012

Thank you so very MUCH!! One question i have is why would i not need the & in front of the functions if i declared it as a *fnctPt in the struct? excuse my noobness im still learning pointers..

**oogabooga** · 09-16-2012

You don't need the & in front of the function names because the function name itself is already a pointer. The ampersand is redundant but allowed.

**laserlight** · 09-16-2012

Originally Posted by Samuel Maciel

why would i not need the & in front of the functions if i declared it as a *fnctPt in the struct?

The function name as used in that context has function type. It is converted to to a pointer to the function, except when it is the operand of the unary & operator (and also the sizeof operator). Therefore, if you leave out the & you get a pointer to the function, and if you include the & you still get a pointer to the function.

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