Posts by epx • 8,191 points
241 posts
-
0
votes2
answers139
viewsA: Raw socket in C
SOCK_RAW allows both receiving and sending packages. The main utility of SOCK_RAW is to implement new transport protocols in userspace (outside the kernel). For example, a program that uses ICMP…
-
3
votes2
answers57
viewsA: Reference is making a variable change the value of another
Why should it be null if you assigned 2? When you did const params = Parametros you just created another reference to the same object. The reference will be const(ante), but the object will not. The…
-
0
votes1
answer47
viewsA: Delete from duplicate records
This command seems to do what you want: delete res1 from REGISTRO res1 inner join REGISTRO res2 where res1.numero = res2.numero and (res1.dt_data < res2.dt_data or (res1.dt_data = res2.dt_data…
-
10
votes2
answers764
viewsA: What is the difference between a map, a dictionary, an associative array and a hash table?
Associative array (Javascript, PHP), dictionary (Python) and Map (Java, C++) are the same thing. They are also called "hash", but this is a metonym, the hash function is the heart of an efficient…
-
0
votes1
answer100
viewsA: Revert a commit that hasn’t been pushed yet, and with multiple comits waiting to get pushed
You can make a git rebase -i d67a194ca^ and will open a screen where you can change the order of the commits, change the description, etc. It is a very powerful command. From what I understand you…
-
1
votes1
answer42
viewsA: C program working but not continuing, gives error at the end
Just look, this program has numerous errors, clearly you need to study the language from the beginning, before trying to make programs. Verbi gratia: 1) Its function ler_clientes() expects a matrix,…
-
5
votes2
answers139
viewsA: How to test if the free(); function worked correctly?
There’s no way. free() does not return value, therefore has no way to report success or failure. In fact, you can only call free() with a valid pointer, allocated by malloc() and company; or NULL,…
-
2
votes1
answer42
viewsA: How do I remove characters from even positions in a string?
You can use a little trick list: >>> a = "01234567" >>> a[::2] '0246' >>> a[1::2] '1357' I put the 2 options because I don’t know if you consider the first position as odd…
python-3.xanswered epx 8,191 -
0
votes2
answers102
viewsA: How does the pthread_cond_timedwait() function work?
That’s how it works: int main() { pthread_cond_t cond = PTHREAD_COND_INITIALIZER; pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; time_t T; struct timespec t; time(&T); t.tv_sec = T + 2;…
-
3
votes1
answer175
viewsA: Test end of file in C
The problem is that the reading has not yet hit the end of file (EOF) when the loop goes to the third cycle, and feof() still returns FALSE. Testing EOF right after trying to read the first line…
-
1
votes2
answers81
viewsA: What is it, Farmhash?
From what I understand, they’re hashes for non-cryptographic purposes. Like, they might be good for a hashmap, for a database index, but not for encryption. "Common" hashes, in the sense of popular,…
-
0
votes1
answer215
viewsA: Replace letter by position
String in Python is immutable, but you could replace, for example, the 5 position character of a string as follows: s = s[0:5] + c + s[6:] If performance is needed, it is best to use a (mutable)…
-
2
votes1
answer25
viewsA: Error on a JS Promise
You forgot to pass "act" as parameter when calling check(). By using the same name "age" as parameter name in function definition, the parameter "hid" the global variable. Just change line 13 to…
-
2
votes3
answers690
viewsA: What is a mainframe?
The main feature of the mainframe is that it lacked microprocessors, in the style of modern computers. The circuits that constituted the CPU (central Processor Unit) were large and modular,…
-
1
votes1
answer47
viewsA: Complexity of simple algorithm
All f(n) does is return -n. Calculating the negative of a number is a constant complexity operation, it is equal for all numbers. And a constant complexity algorithm (large or small) is O(1).
-
-1
votes4
answers634
viewsA: What is the difference between i += 2 and i = i + 2?
In the case of a number there is not much difference, but if it was a more complex type, it may be that += would be more efficient than + because it does not need to create a new object. For…
-
0
votes1
answer28
viewsA: Function return -0
Ideally you would have put in an example code. But you’re probably using floating point numbers (float or double) and they have two zeros: +0 and -0. Useful for preserving the signal in boundary…
-
0
votes1
answer53
viewsA: What’s wrong with using reinterpret_cast on C++?
With it you can convert a pointer of any type to any other type, it is similar to the cast of normal C, the one with (parentheses*). His main problem(s) is that the compiler has no way of checking…
-
1
votes1
answer39
viewsA: File list gives errors when going through . Decode()
The error is that you are assuming that recv() will only receive bytes sent by a send() command. But TCP doesn’t frame the messages, it’s all a byte casing, so your recv() is getting the file name…
-
1
votes1
answer128
viewsA: Release External Mysql Connection
Change the bind-address to 0.0.0.0, which means "all network interfaces". The value 127.0.0.1 refers to the loopback network interface, which allows only local connection, on the server itself.…
-
1
votes1
answer95
viewsA: Receive data input as Python 3 literal value
If I understand correctly, you want the user to type xbb3 and Python to understand this as a special character, correct? Actually this is just one way to do it, you could adopt any other convention,…
-
1
votes1
answer24
viewsA: Submit data p/ database via SOCK_STREAM
In http_msg, there seems to be a gap between %s and HTTP/1.1 missing. This is enough for the server not to recognize the page you are trying to access. Fixing this example seems to work and the…
-
1
votes2
answers28
viewsA: Adding 0.1 to a setInterval gives rounding problems
This is normal, the cause of this is that floating point is represented internally in binary, and 0.1 is a periodic binary titer. Some simple solutions you can adopt: 1) increment 'total' from 1 to…
-
1
votes1
answer76
viewsA: How to save samples before and after an event in a circular buffer?
I would initially load a 2x block the window size at a time, run the window over the buffer. Then, load 1x more window. Pseudocode, considering a window of 50 samples: byte amostras[100] // carrega…
-
-1
votes1
answer68
viewsA: Doubt about date manipulation using time. h
Try to allocate the tm structures using calloc, or wipe them completely using bzero, the structure has other fields than what you filled in and some dirt in them may be influencing the result.…
-
3
votes2
answers46
viewsA: Android - Is it good practice to use the default.xml strings for national applications?
All XML files are UTF-8, so in theory any file of any language can contain any character. Ideal is that the default language is English, but auto school really is a market that only has in Brazil,…
-
1
votes2
answers80
views -
1
votes2
answers551
viewsA: PHP Warning: mysqli_close() expects Parameter 1 to be mysqli, Boolean Given
Probably mysqli_connect() is failing, which assigns FALSE to the $Conn variable. I suggest putting a test after the connection, something like if (mysqli_connect_errno()) { echo "Falhou ao conectar…
-
1
votes2
answers213
viewsA: Hexagon Grid - return neighbors
I think there are two possible solutions; 1) find a mathematical formula that, based on the size of the super-hexagon, returns the numbers of the neighboring hexagons. It would be very fast, but not…
-
1
votes1
answer61
viewsA: Configure Virtual Web Server
I think you are confusing concepts because you spoke of DNS and most likely the solution of your problem lies in the configuration of the Web server. But the options are as follows:: 1) DNS CNAME -…
-
1
votes1
answer101
viewsA: How to get the Gmail source code using Python3
Not to rain on your parade, but... Sites that use AJAX do not return content in HTML, they generate content dynamically, after loading, using Javascript. You would have to use a radically different…
-
1
votes2
answers208
viewsA: Is it always good to de-locate the memory before a "sudden" output of the program with the Exit function call?
The memory allocated by the program belongs to the process; when the process dies, all the resources used by it are released. So, a short running small program can "relax" in memory management…
-
1
votes5
answers12449
viewsA: How to separate a digit from an integer?
One solution is to divide integer by a power of 10, and use the rest of the split operation by 10. For example, in Python 2 to get the third digit from right to left: >>> 9912345 / 100 % 10…
-
2
votes1
answer3545
viewsA: How to make a query in the database with Javascript?
Your question is a little broad, but come on, it’s a perfectly valid question for a beginner. It is not the language that accesses the database, it is some library or framework made for that…
javascriptanswered epx 8,191 -
-1
votes2
answers217
viewsA: What’s the difference between git reset -- <file_name> and git reset HEAD <file_name>?
Git reset allows you to specify the commit. That’s what you’re specifying in HEAD, because HEAD is the latest commit. It could be any other commit from the past.
-
1
votes2
answers5464
viewsA: Segmentation failure: Recorded core image
Short answer: you are using N to create the matrix x[N] before the value of N is set, so it is random (but usually it will be zero). Declare x[N] after scanf(). In C99 it is allowed to declare…
-
2
votes2
answers120
viewsA: How to format strings and store them in a dynamic vector
Try the asprintf() function, which allocates and returns the buffer needed to accommodate the result. Besides returning the right size, it is much safer. As an extension of GNU libc, you need to…
-
2
votes1
answer1802
viewsA: Dereferencing Pointer to incomplete type
When using the type, you are using "struct cadastro", when you should only use "cadastro", since the registration type is already properly defined as struct. If the struct were defined this way:…
-
0
votes1
answer91
viewsA: Extract the cover of an MP3, and other information with PHP
What you need is a library or function that reads the ID3 tags of an MP3 file. It seems to have something in the standard PHP library itself: http://php.net/manual/en/function.id3-get-tag.php…
-
2
votes2
answers607
viewsA: Is it possible somehow to overload functions in C?
In C, no. In C++, yes. You can develop in "C" and compile as C++ just to use the C++ resources that interest you, in the case of function overload.
-
6
votes1
answer4020
viewsA: Maximum character limit of an e-mail address
RFC 5321 specifies (section 4.5.3): maximum 256 characters for a complete email. Other limits: 255 for the domain, 64 for the username (part that comes before the @). However, the recommendation is…
-
-1
votes3
answers5033
viewsA: Use UTF-8 or Latin1?
In Mysql you have the types MEDIUMTEXT (16M characters) and LONGTEXT (4B), so there is no need to worry about limitations imposed by encoding. Standardize in UTF-8 and be happy :)
-
2
votes1
answer82
viewsA: How to start Python code correctly
You mean this test? if __name__ == "__main__": # faz algo What this test determines is whether the execution is happening on main scope, i.e., it is the script that was directly executed from the…
-
3
votes2
answers254
viewsA: Create files in the Home folder with C++
You can uasr the function getenv() to get the value of $HOME: const char* s = getenv("HOME");
-
1
votes1
answer543
viewsA: How can I kill a Thread
Thread doesn’t kill itself, it has to stop on its own, so you don’t escape using a signal or flag mechanism.
-
0
votes1
answer131
views -
7
votes2
answers1076
viewsA: What is Microsoft Access for?
MS-Access is more or less equivalent to Excel and Word, but for database. It has its own database format (MDB) where data, screens, reports, programs, etc. come together. But it can also be client…
-
5
votes2
answers15220
viewsA: How to clear the screen in C++?
Deleting the screen is an operation dependent on the environment in which the program operates. For example, a graphical program does not even have this operation, because it is not running in a…
-
0
votes1
answer35
viewsA: Call to the system dup2 vs. write&read
pipe() seems to be being used correctly in the code. The goal of dup2() is to duplicate the file Descriptor to a set number. In the case of code, the child-process is putting a pipe in place of file…
-
6
votes2
answers104
viewsA: Is there a performance benefit in replacing the operator "==" with the operator "=="?
I did a little test on Node.js V9.8.0: "use strict"; let t0, t1, dummy; t0 = (new Date()).getTime(); dummy = true; for (let i = 0; i < 10000000; ++i) { let j = "" + i; let k = 0 + i; dummy =…