Comparison operators, as their name implies, allow to compare two values and usually return Boolean value (true or false).
Questions tagged [comparison-operators]
658 questions
1664
votes
25 answers
How to check if the string is empty?
Does Python have something like an empty string variable where you can do:
if myString == string.empty:
Regardless, what's the most elegant way to check for empty string values? I find hard coding "" every time for checking an empty string not as…
Joan Venge
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1663
votes
2 answers
Difference between == and === in JavaScript
What is the difference between == and === in JavaScript? I have also seen != and !== operators. Are there more such operators?
Shiva
- 17,795
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482
votes
8 answers
Why does "not(True) in [False, True]" return False?
If I do this:
>>> False in [False, True]
True
That returns True. Simply because False is in the list.
But if I do:
>>> not(True) in [False, True]
False
That returns False. Whereas not(True) is equal to False:
>>> not(True)
False
Why?
Texom512
- 4,361
- 2
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279
votes
6 answers
What is the Ruby <=> (spaceship) operator?
What is the Ruby <=> (spaceship) operator? Is the operator implemented by any other languages?
Justin Ethier
- 122,367
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171
votes
12 answers
162
votes
5 answers
Difference between "!==" and "==!"
Yesterday I stumbled over this when I modified PHP code written by someone else. I was baffled that a simple comparison (if ($var ==! " ")) didn't work as expected. After some testing I realized that whoever wrote that code used ==! instead of !==…
Gerald Schneider
- 16,520
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154
votes
4 answers
Is the operation "false < true" well defined?
Does the C++ specification define:
the existence of the 'less than' operator for boolean parameters, and if so,
the result of the 4 parameter permutations?
In other words, are the results from the following operations defined by the…
duncan
- 2,233
- 2
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- 21
146
votes
1 answer
Find substring in the string in TWIG
I want to find substring of the string or check if there is no such substring using Twig. On the words, I need analogue of 'strstr' or 'strpos' in php.
I googled and searched this issue in stackoverflow but nothing found. Does someone know how to…
user1440167
- 1,683
- 2
- 11
- 12
106
votes
8 answers
No == operator found while comparing structs in C++
Comparing two instances of the following struct, I receive an error:
struct MyStruct1 {
MyStruct1(const MyStruct2 &_my_struct_2, const int _an_int = -1) :
my_struct_2(_my_struct_2),
an_int(_an_int)
{}
std::string…
Jonathan
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60
votes
1 answer
Why does C++11 contain an odd clause about comparing void pointers?
While checking the references for another question, I noticed an odd clause in C++11, at [expr.rel] ¶3:
Pointers to void (after pointer conversions) can be compared, with a result defined as follows: If both
pointers represent the same address or…
Matteo Italia
- 115,256
- 16
- 181
- 279
58
votes
10 answers
Detecting negative numbers
I was wondering if there is any way to detect if a number is negative in PHP?
I have the following code:
$profitloss = $result->date_sold_price - $result->date_bought_price;
I need to find out if $profitloss is negative and if it is, I need to echo…
BigJobbies
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58
votes
3 answers
How is the three-way comparison operator different from subtraction?
There's a new comparison operator <=> in C++20. However I think in most cases a simple subtraction works well:
int my_strcmp(const char *a, const char *b) {
while (*a == *b && *a != 0 && *b != 0) {
a++, b++;
}
// Version 1
…
iBug
- 30,581
- 7
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- 105
56
votes
10 answers
What does "===" mean?
I've noticed someone using the PHP operator === which I can't make sense out of. I've tried it with a function, and it corresponds in crazy ways.
What is the definition of this operator? I can't even find it in the declaration of PHP operators.
Stefan Konno
55
votes
2 answers
Why is "!=" used with iterators instead of "<"?
I'm used to writing loops like this:
for (std::size_t index = 0; index < foo.size(); index++)
{
// Do stuff with foo[index].
}
But when I see iterator loops in others' code, they look like this:
for (Foo::Iterator iterator = foo.begin();…
Maxpm
- 20,568
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53
votes
0 answers
Removed operator!= in C++20 standard library
According to cppreference, the operator!= of many standard library types, including std::unordered_map::operator!= and std::unordered_set::operator!= is removed in C++20.
What is the committee's rationale behind the decision? Won't this make the…
plasmacel
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