Magic numbers are unexplained values that often should be replaced with a named constant.
Questions tagged [magic-numbers]
193 questions
608
votes
15 answers
What is a magic number, and why is it bad?
What is a magic number?
Why should it be avoided?
Are there cases where it's appropriate?
Adam Davis
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556
votes
7 answers
Is 23,148,855,308,184,500 a magic number, or sheer chance?
News reports such as this one indicate that the above number may have arisen as a programming bug.
A man in the United States popped out
to his local petrol station to buy a
pack of cigarettes - only to find his
card charged…
Roddy
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314
votes
2 answers
What does the constant 0.0039215689 represent?
I keep seeing this constant pop up in various graphics header files
0.0039215689
It seems to have something to do with color maybe?
Here is the first hit on Google:
void RDP_G_SETFOGCOLOR(void)
{
Gfx.FogColor.R = _SHIFTR(w1, 24, 8) *…
crush
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124
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The cause of "bad magic number" error when loading a workspace and how to avoid it?
I tried to load my R workspace and received this error:
Error: bad restore file magic number (file may be corrupted) -- no data loaded
In addition: Warning message:
file ‘WORKSPACE_Wedding_Weekend_September’ has magic number '#gets'
Use of save…
N Brouwer
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115
votes
3 answers
Magic number in boost::hash_combine
The boost::hash_combine template function takes a reference to a hash (called seed) and an object v. According to the docs, it combines seed with the hash of v by
seed ^= hash_value(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
I can see that this…
Fred Foo
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27
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11 answers
What are "magic numbers" in computer programming?
When people talk about the use of "magic numbers" in computer programming, what do they mean?
ckv
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27
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3 answers
guess what 0x564c is?
when i read linux kernel source, i found one line says:
#define NCP_SUPER_MAGIC 0x564c /* Guess, what 0x564c is :-) */
(564c)16 = (22092)10 = (53114)8 = (101011001001100)2
Wolfram|Alpha tells us that 22092 = 2^2 * 3 * 7 * 263 = 43…
Ted Yu
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27
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3 answers
HowTo extract MimeType from a byte[]
I've a web page that that can be used to upload files.
Now I need to check if the file type is correct (zip, jpg, pdf,...).
I can use the mimeType that comes with the request but I don't trust the user and let's say I want to be sure that nobody is…
mickthompson
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3 answers
Express.JS: how can I set response status by name rather than number?
OK, everyone knows 200 is OK and 404 is not found. But I for things like permanent vs temporary redirect, or payment required, or other more exotic HTTP error codes, it might be better to do something…
mikemaccana
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1 answer
Is 43679 a magic number?
Recently I was investigating this question: Storing long values in DataGridView C#. After some tests I found out that the DataGridViewCell will not display any text with a length larger than 43679 characters, even if the value is actually stored in…
Alex Filipovici
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17
votes
2 answers
How do I choose a good magic number for my file format?
I am designing a binary file format from scratch, and I would like to include some magic bytes at the beginning so that it can be identified easily. How do I go about choosing which bytes? I am not aware of any central registry of magic numbers, so…
jl6
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How do I get the size of a file in megabytes using Perl?
I want to get the size of a file on disk in megabytes. Using the -s operator gives me the size in bytes, but I'm going to assume that then dividing this by a magic number is a bad idea:
my $size_in_mb = (-s $fh) / (1024 * 1024);
Should I just use…
cowgod
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14
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2 answers
Killing Magic Numbers: "const int" vs "constexpr int" (or is there no difference in the end)
Let's say I have a magic number I want to get rid off...
//whatever.cpp
for (int i = 0; i < 42; i++)
{
//...
}
Reasonably I could kill it in two ways:
Either with const int SOMETHING_SOMETHING_MEANING_OF_LIFE = 42
or with constexpr int…
CharonX
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14
votes
3 answers
How can I say a file is SVG without using a magic number?
An SVG file is basically an XML file so I could use the string
Eduard Florinescu
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4 answers
Why do we need a magic number in the beginning of the .class file?
I read a few posts here about the magic number 0xCAFEBABE in the beginning of each java .class file and wanted to know why it is needed - what is the purpose of this marking?
Is it still needed anymore? or is it just for backwards compatibility now?…
RonK
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