General Q&A about programming, scripting, software design & architecture, process, tools, testing, and more.
In Git documentation, there are lots of references to the term "HEAD". But what exactly is it? Some places refer to it as "a pointer to the current branch". So it's a branch? What is it used for?
What exactly must a C compiler do when it finds a compile-time error? The most obvious kind of errors are language syntax errors, but the C standard also speaks of constraints, which are rules tha...
To protect against dictionary and rainbow table attacks it is well known that passwords should be salted before hashing. The salt (unique to each password) gets stored with the hash, often in the s...
When writing Python-based apps (e.g. Django, Flask, etc.), it's often the case that import statements can be found all over the place, often more than once for the same module. For example, you can...
We have two teams, dev and doc, and I'd like them to have shared access (via git) to a common subset of content. Specifically, I would like the examples that are used in the doc and that are scrip...
I often see the construct if __name__ == '__main__' in Python code. For example, the queens.py demo in the Python repository ends with these two lines: if __name__ == "__main__": main() Ho...
The following list comprehension worked when I tried it: [num for num in hand if num != 11] But this doesn't work: [num for num in hand if num != 11 else 22] which led me to believe that you ca...
When reading questions about C programming from beginners, I very often see them describing peculiar run-time errors and crashes, segmentation faults and similar. They have spent a lot of time chas...
This is intended to be a canonical post for this problem which is pretty common. Especially among beginners. I've heard that I should avoid using floating point variables for representing curren...
I heard rumours that the strcpy function is dangerous and shouldn't be used. Supposedly it can be exploited to create buffer overflows somehow. And indeed when I compile my C code in the admittedl...
Lets say I have two tables, A and B and I need to join a subset of them. Is there best practices of sticking the conditions in the WHERE clause like this, SELECT * FROM A JOIN B on a.fk_b = b....
I spend a lot of time writing CLI tools in Python, and I would like to support tab-completion in a style similar to Git. For example, subcommands should be tab-completable, options should expand ba...
I recently told a friend that malloc(n) allocates and returns a pointer to a block of at least N bytes of memory, as opposed to exactly N; that it is allowed to allocate 'extra' memory to meet e.g....
I have a small new Python 3.8 Flask project with some relative import quirks. For the DB I use SQLAlchemy with Flask-Migrate. My project has the following general structure: controllers/ static/ te...
I'm working on an API to respond some data about a bunch of orders and items. The order and item numbers are always an integer (it's the order.id and item.id value, respectively). Originally the re...
I have created this sensational program: #include <stdio.h> int* func (void) { int local=5; return &local; } int main (void) { printf("%d\n", *func()); } This prints 5 even thoug...
Tldr; I don't need to parse HTML, but I need to check if user submitted input conforms to a very strict subset of HTML. Can regex be a suitable tool for this? Details I have a frontend sanitiser th...
When writing any form of custom function such as this: void func (int* a, int* b) Should I add code to check if a and b are null pointers or not? if(a == NULL) /* error handling */ When po...
Is it correct to destroy a mutex which is referenced but not owned by an unique_lock as in this code? { std::unique_ptr<std::mutex> mutex = std::make_unique<std::mutex>(); std::u...
tl;dr I'd like to learn a compact, cross-compiler way of selectively suppressing compiler warnings. Consider the case where you really mean to make an exact floating-point comparison using ==, o...
I'm using an object-oriented design for my C project and trying to implement classes with private encapsulation. How do I do this? Some things I've tried that are problematic: Using a struct f...
I am developing an application that targets Linux-based OS, and I need to store the user's configuration, metadata and other things in a persistent way (i.e. on the file system). I know that one c...
I've seen some regular expressions (regex) using \s when they want to match a space, but I noticed that it also matches line breaks. Example: the regex [a-z]\s[0-9] (lowercase ASCII letter, follow...
What exactly does the static keyword do in C? I have seen it used in several diverse contexts: 1) As a variable outside a function: #include <stdio.h> static int x = 5; int main (void) ...
Consider the following code: #include <stdio.h> int main() { int a = 5; int b; ++*(&b + 1); printf("%d\n", a); return 0; } The output is as expected: 6 ...
Using Vim, I am trying to search for all instances of a specific string, except for those that fall somewhere in between two other specific strings. For example, I want to determine all instances ...
For some reason, I just wanted to undo a commit on my git repository, which I've done with the following command: git reset --soft HEAD~1 So far, so good. However, by mistake I issued the comma...
How do I delete contents of a specific field, if it matches a pattern, and there is nothing else in the field? I have a several GB tsv file, and I am interested in a specific field (72). If it cont...
I manage a wsgi application that accepts JSON data via POST from potentially untrusted sources. Normally it is treated as a text blob and never parsed, but there is a value in the expected input th...
When reading posts at programming sites such as this one, I frequently encounter people saying things like: "There is no pass-by-reference in C, everything is passed by value." People claiming su...
Consider the following method as an example: List<int> Foo() { // ... } Are there any disadvantages of returning an interface instead of a concrete implementation in C#? IList<i...
Is it valid to partly allocate an object, as long as you only use the allocated part of it? #include <stdio.h> #include <stdlib.h> struct s { int i[100]; }; int main(void) {...
The Problem I have a path optimization problem that in some ways reminds me of the Traveling Salesman Problem, but differs in some key respects. I have a group of items that need to be used by a m...
It is possible to create a new formatter class by subclassing string.Formatter class and then to use it like myformatter.format("{foo:customformat}", foo=foo). It's not super-convenient though, and...
I was fooling around with the following C code on my trusty old x86 PC: #include <stdint.h> #include <stdio.h> int main (void) { uint32_t u32 = 0xAABBCCDD; uint8_t* ptr = (u...
Is uint8_t guaranteed to be a character type if it exists? Will using a uint8_t* to examine bytes of an object cause violation of the strict aliasing rule? Is the following legal code: #include &l...
When discussing best or safest C programming practices with various C gurus on the Internet, the "MISRA-C guidelines for the use of C language in critical systems" often pops up as a source. This ...
What does it mean that we can use memcmp(3) on invalid values? ISO C allows comparing an invalid value through memcmp(3), because it doesn't read the value, but rather its representation, and "rea...
I am working on a website which unfortunately uses a mix of linked and inline CSS and Javascript (and, even more unfortunately, I can't do a lot about the use of inline CSS and Javascript), and am ...
In git I branched feature-A from master. To reduce eventual merge conflicts later, I branched feature-B, which heavily overlaps and depends on A, from feature-A. A build of the feature-B branch s...
To start off, here is the complete HTML of a simple example table: <html lang="en-US"> <head> <title>Title</title> <style> table { width: 20em; ...
I've got this sample regex: Pattern p = Pattern.compile("(?:([aeiou]+)[0-9]+|([123]+)[a-z]+)\\W+"); It basically has the following parts: one or more lowercase vowels ([aeiou]+), followed by one ...
I saw at least one compiler (Codewarrior for HC12) warn me if I use a function without using it's return value. Other compilers (clang/gcc) do not issue a warning though, even when using the std=90...
When I want to print a number or a string, I can use f-strings (Python >= 3.6) or str.format, and I can use just the variable between braces, or use format specifiers. Ex: num, text = 10, 'abc' ...
I'm trying to make a trait method callable on mutable slices of a type implementing that trait (see main). Rust doesn't like me for it. use core::convert::AsMut; trait A { type B; fn f(m: ...
I have developed an Atom package which calls SyncTeX (a utility for reverse lookup for LaTeX), and then opens in Atom the file specified in the SyncTeX response. I'm developing on Linux, but now a ...
From time to time I will have large structural changes to make on my MySQL DB, things like adding columns, changing datatypes, adding indexes etc. These types of changes result in downtime and what...
Let's say I have a script that needs the user to set X number of variables at the start. One can either Pass the arguments in on the command line. Start the program and then have the user input th...
When doing something simple such as this int a=1; int b=2; int c=3; printf("%d\n", a + b * c); then I was told that operator precedence guarantees that the code is equivalent to a + (b * c)...
I'm experimenting with different operators and have a hard time understanding the outcome of certain expressions. I try to combine the ++ operators with other operators such as assignment in the sa...
