strtoul 和 errno

系统为Linux

strtoul 返回的时候，如果输入字串错误或溢出，会设置errno为ERANGE, 如果是过大溢出，则返回值为ULONG_MAX.

不过有一点，就是调用方在调用strtoul之前需要自己手工把errno设为0，这个manpage里说了，不过已开始我没看到，害我折腾了好久。。。

其他类似函数strtol之类应该也是这样吧。

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...

Hardware Password Manager

[Updates 2025-01-20] The original blog post assumes that all passwords are stored in one password manager, and the password manager either unlocks everything or nothing (e.g. Keepass). After discussing with friends, I realized that if I use something like pass , and I use a hardware GPG token, I can actually store and sync all encrypted passwords to all devices, because I will only decrypt the passwords on demand, and the computer will not see the GPG private key. The compromise is that the computer will see the list of all password entries (e.g. accounts), as well as a few other issues . I've been using Keepass for many years. I don't use online password services because I cannot fully trust them. Besides, I may not always have Internet connection, which is why I also don't use a self-hosted service. Everything has been working fine, until I turn my paranoid knob to the max. Here's the thought experiment . The Imaginary Scenario Let's say I have 100 PCs for differe...

Installing Linux on Surface Pro 1g

Windows 10 will soon reach its end of life, and my 1-gen Surface Pro is not supported by Windows 11. I (finally) decided to install Linux to it. Fortunately, it's a not-so-easy nice adventure: The device has only one USB port, so I have to bring back my 10+-year old USB hub. My live USB drive cannot boot directly, I have to disable Secure Boot first, by holding Volume Up during boot. I think years ago I learned that booting on USB might not work through a USB hub, but fortunatelly it worked well with my setup. This is done by holding Volume Down during boot. Wifi adapter was detected in the live Linux environment, but not functional. And I don't have a USB-Ethernet adapter. Luckily, nowadays we have USB-tethering from Android phones, which works out-of-the-box. Originally I planned to following this guide to set up root on ZFS, however, the system froze when building the ZFS kernel module. Then I decided to just use EXT4, yet I still learned a lot from the guide about disk par...

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