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up vote 3 down vote favorite
1

I am new to C++ i am used to PHP and Java. currently for a school project i need to make a function which will be able to return a string array.

Currently i have this in my header.

Config.h

string[] getVehicles(void);

Config.cpp

string[] Config::getVehicles(){
string test[5];
test[0] = "test0";
test[1] = "test1";
test[2] = "test2";
test[3] = "test3";
test[4] = "test4";

return test;}

now obviously this does not work but thats the idea what i am string to do. in Java this would be the way to do it. Ive tried googling my prob but i didnt come across any answers that were clear to be honest.

share|improve this question
    
When you are at, maybe also look at vectors. Easier to use. Because now the caller of getVehicles doesn't know the length of the array. –  RvdK Sep 23 '11 at 10:10

4 Answers 4

up vote 5 down vote accepted

In C++ you don't use an array, but a std::vector instance. Arrays in C++ must have a compile-time fixed length while std::vector instances can change their length at runtime.

std::vector<std::string> Config::getVehicles()
{
    std::vector<std::string> test(5);
    test[0] = "test0";
    test[1] = "test1";
    test[2] = "test2";
    test[3] = "test3";
    test[4] = "test4";
    return test;
}

std::vector can also grow dynamically, so in a C++ program you will find more often something like

std::vector<std::string> Config::getVehicles()
{
    std::vector<std::string> test; // Empty on creation
    test.push_back("test0"); // Adds an element
    test.push_back("test1");
    test.push_back("test2");
    test.push_back("test3");
    test.push_back("test4");
    return test;
}
share|improve this answer
up vote 9 down vote

Maybe it is better to use a vector in this case, but this is not a correct answer for the question. The reason why it doesn't work is that the variable test just exists in the scope of your function. So you have to manage the memory on your own. Here is an example:

string* getNames() {
 string* names = new string[3];
 names[0] = "Simon";
 names[1] = "Peter";
 names[2] = "Dave"; 

 return names;
}

In this case you return a pointer of the position in the heap. All the memory in the heap has to free manually. So it is now your work to delete the memory, if you don't need it anymore:

delete[] names;
share|improve this answer
    
+1 for being the only answer that actually answers the question –  Steve Jun 22 '13 at 4:15
    
Now, how do I find the length of returned array? –  thefourtheye Aug 24 '13 at 3:48
up vote 5 down vote

Use a std::vector<std::string>. It's much easier to deal with than C-style arrays.

#include <string>
#include <vector>

...

std::vector<std::string> Config::getVehicles()
{
  std::vector<std::string> data;
  data.push_back("hello");
  ...
  return data;
}

Check out the other containers in the standard library, they are almost always a better choice than plain arrays in C++.

If your getVehicles method doesn't change the Config object's state, consider making it const:

std::vector<std::string> Config::getVehicles() const { ... }
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up vote -1 down vote

I think this is good way to return STL collection:

#include <string>
#include <vector>

void Config::getSimpleCollection(std::vector<std::string>& out)
{
  // Reserve it if you know good size
  out.reserve(255);
  out.push_back("hello");
  ...
}

Also if you want to return you Config::member you can use another way:

const std::vector<std::string>& Config::getSimpleCollection() const {
    return myField;
}

This way more efficient and you don't copy your vector data.

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