A type conversion where the destination type which cannot represent all values in the source type.
Questions tagged [narrowing]
167 questions
6
votes
3 answers
Is it possible to avoid static_cast in initializer list?
In my code base I often initialize array or vector if bytes using the following the syntax:
uint16_t foo = 0xAB, bar = 0xCD
// bytes = { 0xA, 0xB, 0xC, 0xD }
std::array bytes = {{
foo >> 8,
foo & 0x00FF,
bar >> 8,
bar &…
AMDG
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- 1
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6
votes
1 answer
TypeScript type inference/narrowing challenge
I'm currently trying to improve the types on some existing code. My code looks roughly like this:
/* dispatcher.ts */
interface Message {
messageType: string;
}
class Dispatcher {
on<
MessageType extends…
Pat
- 138
- 4
6
votes
0 answers
narrowing conversion from 'int' to 'double' and array initialization
The following
int i = 0;
double d{i};
gives an error (in clang) or warning (in gcc) of a narrowing conversion from 'int' to 'double'. I found it amazing that this is really narrowing, at least until I saw narrowing conversion from unsigned to…
iavr
- 7,547
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- 53
5
votes
1 answer
Why "key in myObject" does not narrow the type if key is of type string?
I don't understand this:
const VALUES = {
name: "name",
age: "age",
address: "address",
};
export function getVal(key: string) {
if (key in VALUES) {
// Element implicitly has an 'any' type because expression of type 'string' can't be used…
luismartinezs
- 199
- 1
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- 11
5
votes
4 answers
Difference between narrowing and truncation in C++?
I've been going through a book (C++ Programming Language Stroustrup 4th ed).
An example given in a section related to Initialization as below:
void f(double d, int i)
{
int a{ d }; // error : possible truncation
char b{ i }; // error…
pasha
- 2,035
- 20
- 34
5
votes
4 answers
Hidden narrowing conversion from int to uint8_t
Consider the following piece of code:
#include
class A
{
public:
explicit A(uint8_t p_a){ m_a = p_a; };
uint8_t get_a() const {return m_a;}
private:
uint8_t m_a;
};
int main()
{
A a {0x21U};
A aa{0x55U};
…
BobMorane
- 3,870
- 3
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- 42
5
votes
3 answers
How can I detect whether a type is list-initializable?
Background: I'm writing a wrapper type like Either, and I'd like return {some, args}; to work from a function returning Either exactly when it'd work from a function returning A or B. However, I also want to detect when both A and B…
jtbandes
- 115,675
- 35
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- 266
5
votes
1 answer
Strange behavior of narrowing in context of initializer lists
Does someone knows why this compiles without warnings
int main()
{
const int i = 1024;
std::initializer_list i_l = { i }; // no warning
return 0;
}
but does not
int main()
{
const int i = pow(2,10);
std::initializer_list…
abraham_hilbert
- 2,221
- 1
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- 30
5
votes
2 answers
G++ 4.5 Bug: No diagnostic for narrowing in initializer list
I tried the following code:
int main()
{
int x {23.22};
}
which includes an initialization that requires narrowing, but the code compiles fine without any error or warning. On the other hand, the following code gives error:
int main()
{
int…
Saurabh Manchanda
- 1,115
- 1
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- 21
5
votes
4 answers
C++11: "narrowing conversion inside { }" with modulus
I try to compile the following code with gcc and C++11 enabled:
unsigned int id = 100;
unsigned char array[] = { id % 3, id % 5 };
I get these warnings:
narrowing conversion of ‘(id % 3u)’ from ‘unsigned int’ to ‘unsigned char’ inside { }…
m.s.
- 16,063
- 7
- 53
- 88
4
votes
1 answer
Get Narrow Type from Object of Methods
I want to get a Narrowing type like this:
type Expected = {
method: 'firstNamespace/firstMethod'
payload: [string]
} | {
method: 'firstNamespace/secondMethod'
payload: [number, number]
} | {
method: 'secondNamespace/firstMethod'
…
Katarn
- 43
- 3
4
votes
1 answer
How to get clang to warn about very simple narrowing
If I am using clang tools, what is the recommended way to get clang or some part of the clang toolchain to tell me that e.g. passing an int to a function that takes a short might be a bad idea?
Given this very simple program
static short sus =…
Chip Grandits
- 317
- 1
- 9
4
votes
1 answer
Why doesn't braced initialization throw a narrowing error when converting from double to float?
Two things every C++ tutorial mentions early on:
Braced initialization is generally superior when possible, because it will throw an error during a narrowing conversion such as
int narrow{1.7}; // error: narrowing conversion of '1.7e+0' from…
JMA
- 334
- 1
- 9
4
votes
1 answer
Narrowing conversion from char to double
Why there is a warning
narrowing conversion from char to double
I know already that for const char there will be no warning. There are a lot of answers about that. But I would like to know, why for non-const char there is a "might-narrow"…
Wichr
- 43
- 3
4
votes
2 answers
P0960, Is there any kind of mechanic to detect if there are narrowing in the new aggregates init with ()s in c++20?
With P0960 "Allow initializing aggregates from a parenthesized list of values", you can do aggregates init with ()s also.
However, this initialization allows narrowing while {}s doesn't.
#include
#include
struct Foo
{
int x,…
sandthorn
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