Is it possible to use boost::foreach with std::map?
boost, c++, foreach
Solution
You need to use:
typedef std::map<int, int> map_type;
map_type map = /* ... */;
BOOST_FOREACH(const map_type::value_type& myPair, map)
{
// ...
}
The reason being that the macro expects two parameters. When you try to inline the pair definition, you introduce a second comma, making the macro three parameters instead. The preprocessor doesn't respect any C++ constructs, it only knows text.
So when you say `BOOST_FOREACH(pair<int, int>, map)`, the preprocessor sees these three arguments for the macro:
1.`pair<int` 2. `int>` 3. `map`
Which is wrong. This is mentioned in the for-each documentation.
Problem
I find boost::foreach very useful as it saves me a lot of writing. For example, let's say I want to print all the elements in a list: ``` std::list<int> numbers = { 1, 2, 3, 4 }; for (std::list<int>::iterator i = numbers.begin(); i != numbers.end(); ++i) cout << *i << " "; ``` boost::foreach makes the code above much simplier: ``` std::list<int> numbers = { 1, 2, 3, 4 }; BOOST_FOREACH (int i, numbers) cout << i << " "; ``` Much better! However I never figured out a way (if it's at all possible) to use it for `std::map`s. The documentation only has examples with types such as `vector` or `string`.