More C++ Notes

Started to relearn C++ again:

Here are some things I wish to note:

using namespace FRN_MAIN
- using software components from the FRN_MAIN libaries
- makes the libaries + functions unique from other libs. Good for libs that have the same method / function names--> so qualifiy the name space.
- Each namespace defines a scope where global ident + global variables are place

You can also explicitly use the name space in the manor of
namespace _name::member

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Note on Extern

extern "C" function prototype
extern "C" function { blocks }
- tell the compiler do not compile the extern in C++ do it at the linker level.

Polymorphism / Dynamic allocated Objects
virtual
-Destructors
- in an inherited situation calling delete on an object will use the base class destructor use virtual to get around this issue.

Intresting subquery

Intresting query to make a sub select. For 4.0.x you'd need a temporary table instead of the subselect: CREATE TEMPORARY TABLE tmp AS SELECT x1.category, x1.itemid, COUNT(x2.category) AS rank FROM mytbl x1 LEFT JOIN mytbl x2 ON x2.category = x1.category AND x2.itemid = x1.itemid AND x2.timemodified < x1.timemodified GROUP BY x1.category, x1.itemid; SELECT r1.* FROM mytbl r1 JOIN tmp r2 ON r2.category = r1.category AND r2.itemid = r1.itemid ORDER BY r1.category, r2.rank DESC, r1.timemodified DESC;