Yi Wang's Tech Notes

Using Clang: C++0x Features

cxwangyi — Mon, 23 Jan 2012 15:49:11 +0000

I am using Ubuntu Linux 10.10, with which, comes Clang based on LLVM 2.8. When I use Clang to build google-test, it complains that “variadic template” is a C++0x feature and is not yet supported.

However, the Clang installed by Homebrew on my Mac OS X 10.7 (Lion) is based on LLVM 3.0 and works well with google-test.

The homepage of LLVM listed pre-built Clang and LLVM 3.0 for Ubuntu 11.04 and 11.10. So I guess I would have to upgrade to at least Ubuntu 11.04.

FreeBSD 9.0 comes with Clang based on LLVM 3.0.

Python under Linux, Mac OS X and FreeBSD Tells Differently

cxwangyi — Sat, 21 Jan 2012 15:55:28 +0000

It is interesting: under Linux and Mac OS X running on x64 computers, Python 2.7 tells the machine is ‘x64_64′; whereas under FreeBSD, Python 2.7 tells ‘amd64′. You can try:
import platform platform.machine()

Using Clang: Linkers with Different Platforms

cxwangyi — Fri, 20 Jan 2012 08:55:11 +0000

I am using clang++ as the linker with both Ubuntu Linux and Mac OS X. The Ubuntu version invokes collect2, which has parameters –whole-archive and –no-whole-archive to force linking libraries, whereas the Mac OS X version invokes ld (llvm based), which has -force_load for the same purpose.

Using Clang: Cannot Find Standard C++ Library

cxwangyi — Fri, 20 Jan 2012 07:40:42 +0000

When I use clang as the linker to link a C++ program, it complains cannot find standard symbols like std::cout. But if I use clang++ as the linker, it works. However, on both Ubuntu and Mac OS X, clang++ is just a symbolic link to clang! I guess when clang runs, it checks the name in which it was started and work accordingly.

Using Clang: Cannot Find Standard C++ Header Files

cxwangyi — Fri, 20 Jan 2012 07:15:13 +0000

I got a problem with clang today: it complains cannot find standard C++ header files.

So I used two magic options: clang -v -E, which outputs details about how it tries to find the header files. This reveals that clang finds in /usr/local/c++/4.4.x, but not including /usr/local/c++/4.5.1, which is my only version installed together with GCC 4.5.1.

So, my solution is simply sudo apt-get install g++-4.4. (Note that is not enough to install gcc-4.4, because that does not bring you C++ header files and libraries.)

用Go语言实现Design Patterns

cxwangyi — Sun, 01 Jan 2012 15:05:27 +0000

王海磊提醒我注意一篇论文：GoHotDraw: Evaluating the Go Programming Language with Design Patterns。这篇论文里介绍了作者用 Go 语言实现了三种常见的 design patterns：singleton、adaptor 和 template method。作者说，其实他实现了所有的 23 种 GoF design patterns，文中只说了上述三种。

除了这篇论文，我注意到这篇blog：Design patterns in Go programming language 里，作者介绍了如何用 Go 实现另外三种 design patterns：command, strategy 和 factory。

在我的这篇幻灯片里，我本来试图从 design patterns 如何用 Go 实现的角度来介绍 Go 语言。但是因为总结的不够，所以没有这么写。希望接下来能总结一下如何使用 Go 语言。

当然，纯粹的考虑一种语言如何实现一种 pattern 是机械的。一种观点是：如果需要一种 pattern，则说明使用的语言缺乏对应的语法。比如，这篇题为 The (lack of) design patterns in Python 幻灯片里，作者 Joe Gregorio 展示了一些用 Java 和 C++ 需要专门描述的 designs，如果用 Python，则只需少数几行，以至于没必要总结成一种 pattern。

在我的这篇博文里，列了 Peter Novig 的一个幻灯片，其中说 23 种常见 design patterns 中的 16 种，在 Lisp 语言种都有语法可以支持。

Latent Dirichlet Allocation: The Gritty Details

cxwangyi — Sun, 01 Jan 2012 03:54:40 +0000

This is my learning note on the LDA model: Latent Dirichlet Allocation: The Gritty Details

A Learning Note on Go

cxwangyi — Tue, 13 Dec 2011 10:09:07 +0000

This deck is my learning note about the Go programming language: Ready To Go? .

Get Back from the Other Side of GFW

cxwangyi — Sun, 11 Dec 2011 08:44:20 +0000

Once again, wordpress.com was blocked at where I live. And I have been forbidden to update this pure technical blog for two months. Anyway, the good thing is I am back.

To make this post technical, here follows a pretty PDF library written in Go: bitbucket.org/zombiezen/gopdf/pdf, and an ldd implementation in Go https://bitbucket.org/rminnich/ldd/overview.

My Common Lisp Programming Environment

cxwangyi — Fri, 07 Oct 2011 13:12:51 +0000

Just for fun, I want to try Common Lisp. (I’ve been using Scheme when I was a student.)

As an ancient language, CL has many implementations. Following Wikipedia, I chose SBCL, a descendent of CMUCL.

It it just like Eclipse for Java, Emacs + SLIME is powerful for Common Lisp (or Scheme). Auto-complete and other stuff are so well supported.

dpans2texi enables us to get help about the word under cursor by simply typing ‘C-h S’.