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authorBrook Zhou <zz3599@yahoo.com>2015-10-31 16:17:58 -0700
committerBrook Zhou <zz3599@yahoo.com>2015-10-31 16:27:42 -0700
commitc3e769e4ac50d4475a530969663e073f4ff002ca (patch)
tree45a68dbe1c1d62b1ee8abf900687976c1f99dc65
parent5b0db44e7c5f0a69dfa670eee13fbc011f76830a (diff)
[cpp/en] comparator function for std containers
-rw-r--r--c++.html.markdown18
1 files changed, 18 insertions, 0 deletions
diff --git a/c++.html.markdown b/c++.html.markdown
index d03092e5..6b452b1b 100644
--- a/c++.html.markdown
+++ b/c++.html.markdown
@@ -801,6 +801,24 @@ void doSomethingWithAFile(const std::string& filename)
// all automatically destroy their contents when they fall out of scope.
// - Mutexes using lock_guard and unique_lock
+// containers with object keys of non-primitive values (custom classes) require
+// compare function in the object itself or as a function pointer. Primitives
+// have default comparators, but you can override it.
+class Foo {
+public:
+ int j;
+ Foo(int a) : j(a) {}
+};
+struct compareFunction {
+ bool operator()(const Foo& a, const Foo& b) const {
+ return a.j < b.j;
+ }
+};
+//this isn't allowed (although it can vary depending on compiler)
+//std::map<Foo, int> fooMap;
+std::map<Foo, int, compareFunction> fooMap;
+fooMap[Foo(1)] = 1;
+fooMap.find(Foo(1)); //true
/////////////////////
// Fun stuff