Pointer to pointers

[jyngem]

I'm trying to implement a list of functions together with their names, like this: typedef struct BinaryFunction { double (*eval)(double, double); char* sign; }; double add(double a, double b) { return (a+b); } char addSign[] = " + "; BinaryFunction Add = { add, addSign }; Finally, the pointe: BinaryFunction** bFunctionList; How do I initialize/use this last pointer?

[HJo]

This is one way of doing it... struct BinaryFunction { double (*eval)(double, double); char* sign; }; double add(double a, double b) { return (a+b); } double subtract(double a, double b) { return (a-b); } int main(int argc, char* argv[]) { BinaryFunction** ppBFunctionList = new BinaryFunction*[2]; char addSign[] = " + "; BinaryFunction Add = { &add, addSign }; ppBFunctionList[0] = &Add; char subSign[] = " - "; BinaryFunction Sub = { &subtract, subSign }; ppBFunctionList[1] = ⋐ for (int i = 0; i < 2; i++) { double dRes = (*ppBFunctionList[i]->eval)(3, 2); printf("%.2f\n", dRes); } return 0; } Regards, /Henrik J

[Iain Clarke Warrior Programmer]

I presume you want something like:

main ()
{
BinaryFunction f [] = { {Add, "+"},
{ Subtract, "-"},
{ Power, "pow"},
{ NULL, NULL}
};

double dEval1 = DoAFunctionOne ("Add", 1.0, 2.0, f)
double dEval2 = DoAFunctionTwo ("Add", 1.0, 2.0, &f)

}

double DoAFunctionOne (char *name, double A, double B, BinaryFunction *func)
{
while (func && func->sign)
{
if (!lstrcmpi (name, func->sign))
{
if (!func->eval)
break;
return func->eval (A,B);
}
func++; // Move on to the next one...
}

// Raise an exception?
return 0.0;

}
double DoAFunctionTwo (char *name, double A, double B, BinaryFunction **func)
{
for (int n = 0; func && func [n]->sign; n++)
{
if (!lstrcmpi (name, func->sign))
{
if (!func [n]->eval)
break;
return func [n]->eval (A,B);
}
}

// Raise an exception?
return 0.0;

}

Having typed this all, I've got a sneaking suspicion I've just done your homework. If I'm right, take this as an example of how these things work. If you hand it in as your own work then your teacher will become suspicious... If I'm wrong, then I apologise! Iain.