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Showing posts from April, 2023

Difference Between the clear Command in Linux and Mac

I've been writing a series of posts about CSI Sequences, but we rarely use CSI Sequences directly. However, there is a CSI Sequence that we use unknowingly. It's the clear command that clears the screen. The clear command basically uses two types of CSI sequences. One is CSI H ( Cu rsor P osition, a.k.a CUP); it moves the cursor to the beginning of the screen. The cursor is at the top-left corner after the command ends, thanks to CUP. The second CSI Sequence is CSI 2 J ( E rase in D isplay, a.k.a. ED), which is used to clear the entire screen. Linux and Mac use these two sequences; they behave the same way up to this point. However, Linux's clear and Mac's differ in their subsequent actions. In a nutshell, Linux's clear clears the scrollback buffer, while Mac's does not. Linux's one prints CSI 3 J after the two sequences. CSI 3 J is an extension of the Escape Sequence introduced by xterm that removes lines stored in the scrollback buffer. Since be

What is the size of an empty object?

Consider a class like the one above. Commonly called an "empty class," this class has no internal variables. So, how big is this empty class? At first glance, the size should be 0 since there are no member variables. However, the size is never 0 in any language, whether Java, C#, C (in this case, a struct), or C++. This is to ensure that two different objects never have the same address. Empty classes typically have a size of 1 byte in a 32-bit environment and 2 bytes in a 64-bit environment. However, the exact size cannot be determined. According to the specification, the size just needs to be non-zero. The precise size depends on the implementation. This is a translation of my old Korean post written in 2015. Because the size can vary depending on the implementation, it is now possible to have different sizes (although still not 0). And Languages like Rust have even introduced zero-sized types . We will look at this topic in more detail at a future opportunity.

Clear Screen with CSI Sequence

Today, following my previous post , I will explain how to clear the screen using CSI Sequences. There are two sequences in the CSI Sequence for clearing. The first one is the Erase in Line sequence, called EL . It is composed of CSI # K ; it is used to erase lines, as the name suggests. If the # is not provided, the default value is 0, and if a value is provided, it must be one of the three: 0, 1, or 2. The terminal will ignore the sequence if any other value is provided. For example, if you print 0x311b5b334b32 (or 1^[3K2 ), the terminal ignores ^[3K , and the screen displays only 12 . The behavior of 0, 1, and 2 can be summarized as follows. 0 Erases from the cursor to the end of the line. 1 Erases from the beginning of the line to the cursor. 2 Erases the entire line, regardless of the cursor's position. Remember that the EL sequence does not move the cursor's position. Therefore, if you want to erase the current line and write a new line on the c

[C++] Handling Exceptions in Constructors

When you use RAII idiom, there are often situations where constructors have to do complex tasks. These complex tasks can sometimes fail, resulting in throwing exceptions. This raises a concern: Is it okay to throw exceptions in constructors? The first concern is memory leaks. Fortunately, memory leaks do not occur. Variables created on the stack are released through stack unwinding, and if an exception occurs during heap allocation with the new operator, the new operator automatically deallocates the memory and returns nullptr . The next concern is whether the destructor of the member variables will be called correctly. However, this is also not a problem. When an exception occurs, member variables can be divided into three categories: fully initialized member variables, member variables being initialized, and uninitialized member variables. Fully initialized member variables have had their constructors called and memory allocations completed successfully. In the example code, t

[C++] enum class

Traditional C++ enum had several issues. To solve these problems, C++11 introduced a new feature called enum class . In this article, I will examine the problems with the traditional enum and how they are solved with enum class . First, traditional enum could not be forward-declared. The reason was that if the values in the enumerator were unknown, it was impossible to determine their size . However, enum class is treated as int if an underlying type is not specified, assigning values outside the range of an int will raise a compilation error. If you want to use values outside the range of an int , you need to specify the underlying type. Another problem with traditional enum was that the scope of enumerator names was not limited. Let's see the following example. Here, we try to represent the results of IO and Parse functions with enum s. However, this code will not compile because the Error and Ok of IOResult conflict with those of ParseResult . To resolve t