macro for looping through a templated map

Is it possible to make a macro to loop through any kind of maps?

Normally, it's

Code:

map<int, string>::iterator it;
for(it = somemap.begin(); it != somemap.end(); it++){
   // do schtuff
}

For an xml class I have, I've actually made some looping macros which replaces

Code:

int i;
for(i = 0; i < xmlnode.size(); i++){
   xmlnode& tec = xmlnode[i];
   // do schtuff
}

into

Code:

xmlloop(xmlnode)
   // do stuff with "tec" as a xmlnode&
xmlloopend

So yeah, can the same be done with maps without having to specify their types? that is, I don't want:

Code:

maploop(int, string, somemap)
   // do stuff with it, which is an iterator..
maploopend

You could take a look at Boost.Foreach. In the next version of C++, there will probably be a range based for loop that would make this redundant.

Of course, you could also consider applying an appropriate generic algorithm instead of using a convenience macro.

Shouldn't std::for_each() work too?

Originally Posted by cpjust

Shouldn't std::for_each() work too?

That is what I mean by "applying an appropriate generic algorithm", though I hope that an even more appropriate algorithm is chosen, if feasible (or maybe a std::map specific algorithm should be used). The Boost.Foreach documentation notes that this "forces us to move our logic far from where it will be used", unless lambda expressions are used.

I see.. even with combining a #define macro with for_each it will still need to know the type.. I guess it's probably good for type checking.

anyways thanks!

Originally Posted by underthesun

even with combining a #define macro with for_each it will still need to know the type..

If you are going to restrict the usage to std::map (or perhaps to standard library containers in general), then this is not necessary since value_type typedef in the scope of the std::map would provide the necessary type information. However, you would then loose the covariance feature provided by BOOST_FOREACH, although you gain in convenience.

Hmm.. care to explain that last bit? How exactly do I use value_type for automatically getting an iterator type given a map?

Code:

map<int, int> themap;

themap::iterator it; // <-- is this where I can use value_type somehow?
for(it = themap.begin(); it != themap.end(); it++){
   blah();
}

hmm... looks like I am wrong. Since one cannot use a function template, the value_type macro is not useful, since one still needs to provide the type of the container to the macro in order to access it.