Questions tagged [constexpr-function]
42 questions
1
vote
1 answer
c++ how to use constexpr value with operator []
The origin problem is I want to use const char* or char [] in template non-type arguments. Of course it is not supported now. So I want to write some code to convert char[] to std::integer_sequence. But I found a seriously…
blackshadow
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0
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0 answers
how to make a field of a constexpr object constexpr too?
cube is a class that from what i know can be both constexpr and not and for some reason c.get() is not constexpr because the second cout prints 5 which mean it changed the value of c to 5 instead of c.get() always returning 1.
class cube
{
private:
…
shar yashuv Giat
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- 1
0
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1 answer
Initialize a pointer with constinit
I was wondering whether I could initialize a pointer with constinit in C++20, and I didn't find any adequate answer on the internet.
I have a simple code like this:
struct a {
const char *s; // pointer I want to initialize
int…
dVNE
- 161
- 9
0
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1 answer
How to check if instances of a class with a constexpr constructor get instantiated at compile time?
How can I check that instances of MyDouble will be created at compile time?
What will happen if I instantiate MyDouble with a non-constant expression?
#include
struct MyDouble{
double myVal;
constexpr MyDouble(double v):…
navid
- 27
- 5
0
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1 answer
confusion about constexpr function body
cppreference said the following about the body of a constexpr function:
the function body must not contain:
a definition of a variable of non-literal type
a definition of a variable of static or thread storage duration.
All I understood about a…
mada
- 1,646
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0
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1 answer
literal type in constexpr expression and template parameter
Why do I can use non constexpr literal types in constexpr functions(such as reflection) and it can be returned as constexpr, but I can't use such types in template non-type parameters?
class Point {
public:
constexpr Point(double xVal =…
Vanconts
- 45
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0
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1 answer
What is the advantage of constexpr virtual functions in C++20?
I can easily say that by declaring a function as constexpr, we evaluate it during the compile-time and this saves time during run-time as the result was already produced.
On the other hand, virtual functions need to be resolved during run-time.…
Caglayan DOKME
- 948
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0
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1 answer
static compilation of an instance from json data in rust
I want to create a static instance at compile time (not runtime) from JSON data loaded from a file (similar to constexpr):
Example:
// a file in the project /path/to/project/data.json
{
"field1" : "a"
}
// project code:
use…
Avba
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0
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1 answer
What is preventing compile time evaluation of this constexpr function?
I'm working on a class for representing a set of hardware pins of a microcontroller (STM32). The selected pins may be discontinuous on the port, but they are assumed to be ordered. For example, if this PortSegment object is created to represent PA2,…
Tagli
- 2,412
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2 answers
How can I initialise a constexpr array with values using std::generate
For example, if I wanted a constexpr std::array initialised with all the multiples of 3 from 1-300 at compile time how can I do this?
My first thought was to use std::generate, something like:
constexpr std::array a {…
nectarine
- 65
- 4
0
votes
1 answer
constexpr string-literal checking: short syntax, no runtime possibility
EDIT: Renamed, as my final solution does not use a poisoning method.
I'm looking for a way to prevent a constexpr method from being called at runtime. I'm writing a function that accepts a string literal, so I cannot simply use a NTTP as a way to…
Sean
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