Improved main-snippet.

snippets/c++-mode/main

@@ -2,9 +2,16 @@
 # name: main
 # key: main
 # --
+#include <string>
+#include <vector>
+
+using std::string;
+using std::vector;
+
 int main(${1:int argc, char *argv[]})
 {
-    ${0:const vector<string> args(argv, argv + argc);}
+    ${2:const vector<string> args(argv, argv + argc);}
+    $0
 
     return 0;
 }