How to create a function with return type map<>?

Fairly straightforward question. I have a map that I wish to initialize by calling a function like so:

map<string, int> myMap;

myMap = initMap( &myMap );

map<string, int> initMap( map<string, int> *theMap )
{
    /* do stuff... */

However, the compiler is moaning. What's the solution to this?

EDIT 1:

I'm sorry, but I screwed 开发者_如何学JAVAup. The code was correctly written with *theMap, but when I posted the question, I failed to notice that I had omitted the *. So to answer the comment, the error message I get is:

1>Roman_Numerals.cpp(21): error C2143: syntax error : missing ';' before '<'

which is thrown at

map<char, int> initMap( map<char, int> *numerals );

using VC++ 2010 Express and the same error again when I define the function.

Either do:

map<string, int> myMap;
initMap( myMap );

void initMap( map<string, int>& theMap )
{
    /* do stuff in theMap */
}

or do:

map<string, int> myMap;
myMap = initMap(  );

map<string, int> initMap()
{
    map<string, int> theMap;
    /* do stuff in theMap */
    return theMap;
}

i.e. let the function initialise the map you give it, or take the map the function gives you. You're doing both (without a return statement too!)

I'd go for the first option.

It's probably complaining because you're passing the address of the map, but your function accepts the map by value.

You might want something more like this:

void initMap(map<string, int>& theMap)
{
    /* do stuff...*/
}

The canonical solution is just

std::map<std::string, int> initMap();
// ...
std::map<std::string, int> myMap = initMap();

Why the tricky attempt to use an input parameter for a return value? Performance? Modern compilers don't care. In fact, not constructing an empty map will be slightly faster.

You should accept a pointer or preferably a reference to the map. You could also return a reference for convenience:

map<string, int>& initMap( map<string, int>& theMap )
...
// Call initMap
map<string, int> my_map;
initMap(my_map);

why not do void initMap(map& theMap), instead of making so many copies of the map?

&myMap is a pointer to a map object, while the argument theMap is a map object.

Two solutions:

Change myMap = initMap( &myMap ); to myMap = initMap( myMap );.

or

Change map<string, int> initMap( map<string, int> theMap ) to map<string, int> initMap( map<string, int> * theMap ).

A bit late to the game but: I would guess from the error message that you're missing out

#include <map>

at the top of your code. So the compiler doesn't know that map is supposed to be a template, and it consequently gets confused by the angle brackets which follow.

 void initMap(map<String,int> &Map)
 {
   //Do something
 }