Pass string value into function as an array

[Spillman]

I'm a new at C++ and need some help with this code. I searched but maybe because I'm not familiar with the correct vocabulary for C++, I couldnt' find an answer for this.

What I'm trying to do is pass a string into a function that is looking for an array.
Probably easier for me to show the code then write it out.

Code begins with AppMain()...

Let's say I have this declaration and 4 arrays:

char * theCategory;

char* arrCats[]={"fruits","veggies","colors"};
char* fruits[]={"Apple","Banana","Berry"};
char* veggies[]={"Asparagus","Bell Pepper", "Carrot","Corn"};
char* colors[]={"Aqua","Black","Blue","Brown","Gray"};

Then I have these 3 functions:

void getCatArrAndVals (char* arg[]) 
{
 //do something
}

char * LoadCategory()
{
	srand( time(NULL) );
	int RandIndex = rand() % 3;
	theCategory=arrCats[RandIndex];  //category I'm interested in
	getCatArrAndVals(colors);  //I'm passing the hard-coded value of "colors" array
                                    //here but I really want to pass theCategory
	return theCategory;
	}

void AppMain()
{
	LoadCategory();
}

How do I pass the string value into the getCatArrAndVals functions as an array?

[Ancient Dragon]

The function wants all of the strings, not just one of them. If you want to pass just a single string then you will have to change the signature of the function to getCatArrAndVals(char *s)

[Spillman]

I'm not sure I made myself clear: I actually DO want to pass the array (with all the strings) and not just one string. For example, if the chosen category is string: "colors," then I want to pass the "colors" array and the values it holds.

[L7Sqr]

theCategory=arrCats[RandIndex];  //category I'm interested in
	getCatArrAndVals(colors);  //I'm passing the hard-coded value of "colors" array
                                    //here but I really want to pass theCategory

The problem with that idea is that colors is a collection of things and theCategory is just a thing. Your function needs to take either a collection or just a thing - but not both. I'd suppose that you may be trying to do the following:

char* arrCats[]={"fruits","veggies","colors"};
char* fruits[]={"Apple","Banana","Berry"};
char* veggies[]={"Asparagus","Bell Pepper", "Carrot","Corn"};
char* colors[]={"Aqua","Black","Blue","Brown","Gray"};
char **groups[] = {arrCats,fruits,veggies,colors}

// and later ...
char ** theGroup = groups[rand() % 4];

Although, with all that pointer nonsense it might be easier to just use std::string and std::vector . For example

std::vector< std::string > colors;
colors.push_back ("Aqua");
colors.push_back ("Black"); 
// and so on for each group you have above

std::vector< std::vector< std::string > > groups

Then you could still get at any of those groups with groups[rand() % 4] but the pointer mess would be gone.

[Spillman]

Thank you for the response, however, when I tried the first example, I was getting back values like "Apple" and other items in the array instead of just the array names (i.e. - Colors, Veggies, Fruits). I suspect the 2nd example will do the same thing. I guess I can always go with a case/switch but it seems so clunky. I was hoping there was a more suave way of doing this.

[Spillman]

Just learned that you can't use case/switch with strings in C++. So... used if/elseif:

if (theCategory=="colors") getCatArrAndVals(colors);
else if (theCategory == "fruits")  getCatArrAndVals(fruits);
else if (theCategory == "veggies")  getCatArrAndVals(veggies);

If anyone has a sleeker way of doing this, please let me know.

TIA

[mrnutty]

Just learned that you can't use case/switch with strings in C++. So... used if/elseif:

if (theCategory=="colors") getCatArrAndVals(colors);
else if (theCategory == "fruits")  getCatArrAndVals(fruits);
else if (theCategory == "veggies")  getCatArrAndVals(veggies);

If anyone has a sleeker way of doing this, please let me know.

TIA

Sure

#include <map>
#include <string>
#include <vector>
#include <iostream>
using namespace std;


typedef std::vector<std::string> StringArray;
typedef void(*FuncPtr)(const StringArray& values);


void getCatArrAndVals(const StringArray& values){
 //do something useful
 for(size_t i = 0; i < values.size(); ++i)
	 cout << values[i] << "\n";
}

struct WrappedFunc{
 StringArray savedArg; //argument to be passed to mappedFunc
 FuncPtr mappedFunc; //mappedFunc to be called
 WrappedFunc(){}
 WrappedFunc(const StringArray& arg, const FuncPtr& fp)
 	 : savedArg(arg), mappedFunc(fp){}
 void operator()(){
	 (*mappedFunc)(savedArg);
 }
};

StringArray createFruits(){
	const char* fruits[]={"Apple","Banana","Berry"};
	return StringArray(fruits,fruits + sizeof(fruits)/sizeof(*fruits));
}
StringArray createVegetables(){
	const char* veggies[]={"Asparagus","Bell Pepper", "Carrot","Corn"};
	return StringArray(veggies, veggies + sizeof(veggies)/sizeof(*veggies));
}
int main(){
 typedef std::map<string,WrappedFunc> StringMappedCallback;
 StringMappedCallback callbacks;
 StringArray fruits = createFruits();
 StringArray veggies = createVegetables();
 callbacks["fruits"] = WrappedFunc(fruits,getCatArrAndVals);
 callbacks["veggies"] = WrappedFunc(veggies,getCatArrAndVals);

 string pickedCatagory = "veggies"; //get input from somewhere
 callbacks[pickedCatagory]();
}

Thats the general idea, but of course you would use something like boost::Function adapted to it.

[Spillman]

Thank you for this. It will be a few days before I have a chance to play with this again but what you wrote looks like just what I needed.