Accessing local variables from void functions - c++

Question

I have two functions that read files and initialize variables containing data parsed from the files read.
These variables include several vectors, counters (line counts) and a few singular variables (string and ints).
The problem I am having is that these variables all need to be accessed in later functions, and the idea is to avoid global variables. Since the functions are void, they cannot return variables, and I have found (unlike my normal language of Python) returning multiple variables is difficult.
What is a better way to go about this?
The vectors in each of the read*() functions need to be accessed in a new function I am building. But I also need the num* variables, and the recipe & serving variables.
EDIT: My code currently
#include <string>
#include <vector>
#include <fstream>
#include <sstream>
#include <iostream>
using namespace std;
void readNutrients(string input_file) {
ifstream in(input_file.c_str());
string line;
vector<string> nName, nUnits;
vector<double> nAmount, nCalories;
string name, units;
double amount, calories;
int numNut = 0;
while (getline(in, line)) {
numNut++;
int pos = line.find(';');
name = line.substr(0, pos);
nName.push_back(name);
line = line.substr(pos + 1);
istringstream iss(line);
iss >> amount >> units >> calories;
nAmount.push_back(amount);
nUnits.push_back(units);
nCalories.push_back(calories);
}
}
void readRecipe(string input_file) {
ifstream in(input_file.c_str());
string line;
string recipe;
vector<string> rName, rUnits;
vector<double> rAmount;
string name, units;
double amount;
double servings;
int numIng = 0;
while (getline(in, line)) {
numIng++;
if (numIng == 1) {
int pos = line.find('\n');
recipe = line.substr(0, pos);
}
else if (numIng == 2) {
istringstream iss(line);
iss >> servings;
}
else {
istringstream iss(line);
iss >> amount >> units >> ws;
rAmount.push_back(amount);
rUnits.push_back(units);
getline(iss, name);
rName.push_back(name);
}
}
}
void readFiles(string nutrientFile, string recipeFile) {
readNutrients(nutrientFile);
readRecipe(recipeFile);
}
int main(int argc, char** argv) {
readFiles(argv[1], argv[2]);
return 0;
}

Answer 1

Since you included your code, I have a better idea of what's going on.
What you need is to create a structure that can hold the result of your parsing. Since your function is not returning anything, it's only logical that you won't have access to it's result.
I think your intent here is to have a list of nutrients read from a file, and read every nutrients from that file and fill up the list in your program.
The problem is that your program has no idea of what makes a nutrient a nutrient. You should teach him that by declaring what makes a nutrient a nutrient:
struct Nutrient {
std::string name, unit;
double amount, calories;
};
Then, instead of creating a bunch of lists of values, you should create a list of nutrients.
std::vector<Nutrient> readNutrients(std::string input_file) {
// Here declare your vector:
std::vector<Nutrient> nutrients;
// declare line, calories, name...
while (std::getline(in, line)) {
// fill your variables name calories etc...
// create a nutrient
Nutrient n;
// fill the nutrient with values from the parsing.
n.name = name;
n.unit = units;
n.amount = amount;
n.calories = calories;
// add the nutrient to the list.
nutrients.push_back(n);
}
// return a filled list of nutrient.
return nutrients;
}
By the way, you don't need the num* variables, since nutrients.size() will return you the number of nutrients in the list.
That solution goes the same with recipes: Create a type to add the concept of a recipe in your program, and use that type.
Please note that this code is not optimal, std::move from C++11 should will grant you enormous speed up.

Answer 2

I don't understand your case clearly. But because you can't get result as return values of void function, it may get results by output arguments using pointers or refrence types.
for example:
void _read(const char* file, vector<string>& r_list, int* pState)
{
// do parsing file
// do outputs
*pState = (your_number);
r_list.push_back("your string");
}
Hope this is useful for you.