How big is a Million Lines of Code?

http://www.embedded.com/columns/technicalinsights/205604461?printable=true

by getp • 19 years ago

20 19 19 years ago

DaniFong• 19 years ago

I read somewhere that the blockbuster title 'Gears of War' had only about half a million lines of C++ code: ~250,000 specific to the game, and ~250,000 for the entire Unreal 3 engine.

I was surprised. Steve Yegge seems to be pretty well known as a programmer, or at least, as a programming blogger, but his 'modest' web game was more than a million lines of Java.

Apparently, if you're disciplined enough (they coded in layers, much of which was in a strictly functional style) you can do a lot with a little.

palish4• 19 years ago

Ah.. Gears of War is also a single player game. Steve's game is closer to an MMO. Once functionality needs to happen across 60 different computers in a synchronized fashion, code can get pretty complicated. And sometimes a multiplayer setting can actually force you to write functionality that only makes sense in a multiplayer setting.

For example, Steve's game levels are tile-based, but I doubt he restarts the server whenever he makes a small change to a level. That means the level needs to be editable at runtime, which means changes need to be streamed dynamically to all clients that might be watching. The changes also need to be serialized to the database periodically, so that they aren't lost when the server does reset.. And you need code to make sure two players' views of that level don't get out of sync if they are both editing it at the same time. That tileset loader code you wrote now needs to be able to support additional tiles at runtime, which means you need a collision tree that can be rebalanced quickly without hogging valuable server resources. And what happens if a player was standing in a valid tile, but you just removed that tile? You get the idea.

My employment's game is easily over a million lines of code at this point, and the client alone is about 700,000. Not only that, but the client is completely recompiled for every change - so it takes about 10 minutes from the time you've made a change until you've tested it. People avoid compiling the engine like a genetically-engineered flesh-eating virus, so you're coding for maybe hours before you test all your changes. And since debugging requires changing code, each mistake costs you another 10 minutes. The whole process is like putting together a 10,000-piece puzzle upside-down.

Some bits of advice for large C++ projects:

* You need to have split your functionality into about 20 different DLLs before you get to the point of being an oh-god-why-is-it-so-massive project.

* You must write most of your objects using the interface pattern (a pure virtual interface in the header file, and your implementation exclusively in the source file). No private function or variable declarations should be written in the header at all. This facilitates extremely fast compile times. Here's an example of what I mean: http://dl.getdropbox.com/u/315/example.cpp

* Sometimes you need to ignore what senior programmers think is best to get your goals accomplished. Remember, they got you into this situation in the first place.

greendestiny3• 19 years ago

Just because you can generate a hypothesis doesn't make something true. Its pretty difficult to compare the difference in required code for a modern 3D engine, with lots of single player functionality like scripting and AI, and a multiplayer game with a lesser graphics engine. It should be noted that there are some simple multiplayer games that are hardly any code at all though. 500k lines all up for Gears of War certainly seems massively less than the industry average for that kind of project.

Just because you like Yegge's post and/or game doesn't mean his code needed to be that big. Judging from his post on code size it's not like he cares particularly.

cperciva• 19 years ago

You need to have split your functionality into about 20 different DLLs before you get to the point of being an oh-god-why-is-it-so-massive project.

How does separating out code into DLLs help? Linking is fast.

You must write most of your objects using the interface pattern (a pure virtual interface in the header file, and your implementation exclusively in the source file).

This is something which you should always do -- not just for large C++ projects. Separating interfaces from implementations is ALWAYS good design.

unexpected• 19 years ago

dude, gears of war is multi-player.

joeguilmette• 19 years ago

a million lines of code? about one 50th of vista.

Xichekolas• 19 years ago

I enjoyed the following at the end of the article (with context added by me):

Think about that last analogy: A million [lines of code costs a million] times the cost of the flash chips [it is stored on]. Yet accounting screams over each added penny in recurring costs, while chanting the dual mantras "software is free," and "hey, it's only a software change."

I've worked at a place like that before. They would pay a full team of developers for several months to roll our own custom solution to something we could have bought off the shelf for $1000. People just don't see software as expensive to develop... and unless it's open source, it is.

tlrobinson• 19 years ago

In most cases: too big.

aswanson• 19 years ago

They need to come up with a new metric. LOC is so wrong for so many reasons. Running tested features seems like a good way to measure project progress but I don't know how it would relate to overall project complexity. http://www.xprogramming.com/Blog/Page.aspx?display=RunningTe...

dfranke• 19 years ago

LOC is a terrible measure of productivity, but as a long-term measure of work it's not so bad.

How big is a Million Lines of Code?

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