using boost foreach with items that are themselves templates - c++

Question

I have a std::deque< std::pair<int, int> > that I would like to iterate over using BOOST_FOREACH.
I tried the following:
#define foreach_ BOOST_FOREACH
// declaration of the std::deque
std::deque< std::pair<int, int> > chosen;
foreach_( std::pair<int,int> p, chosen )
{
...
}
But when I compile this (in Visual Studio ) I get the following errors:
warning C4002: too many actual parameters for macro 'BOOST_FOREACH'
1>c:\users\beeband\tests.cpp(133): error C2143: syntax error : missing ')' before '>'
1>c:\users\beeband\tests.cpp(133): error C2059: syntax error : '>'
1>c:\users\beeband\tests.cpp(133): error C2059: syntax error : ')'
1>c:\users\beeband\tests.cpp(133): error C2143: syntax error : missing ';' before '{'
1>c:\users\beeband\tests.cpp(133): error C2181: illegal else without matching if
What is the correct way to use BOOST_FOREACH with this deque?

Answer 1

The problem is the , as it is being used by the preprocessor to separate the macro arguments.
Possible solutions using typedef:
typedef std::pair<int, int> int_pair_t;
std::deque<int_pair_t> chosen;
foreach_( int_pair_t p, chosen )
// Or (as commented by Arne Mertz)
typedef std::deque<std::pair<int, int>> container_t;
container_t chosen;
foreach_(container_t::value_type p, chosen)
Possible replacements, both introduced in c++11, are:
range-for loop:
for (auto& : chosen)
{
}
lambdas:
std::for_each(std::begin(chosen),
std::end(chosen)
[](std::pair<int, int>& p)
{
});

Answer 2

As the author of BOOST_FOREACH, I ask you to please stop using it. It was a hack whose time has come and gone. Please, please, please use C++11's range-base for loops and let BOOST_FOREACH die.

Answer 3

Boosts foreach is a macro, which means it's handled by the preprocessor. And the preprocessor is pretty simple, and can't handle symbols with commas in them as it is used as a macro argument separator.