80 questions
12
votes
2
answers
1k
views
How can I iterate a flat_map in a range-based 'for' loop, updating values?
It is easy to iterate std::map and update values:
#include <iostream>
#include <map>
int main() {
std::map<int, int> m;
m[1] = 2;
m[2] = 4;
for (auto &[k, v] : m)...
- 425
2
votes
2
answers
160
views
Structured binding for std::views::enumerate of std::map [duplicate]
I'm trying to do something like this:
const std::map<char, int> histogram{
{'A', 2},
{'D', 1},
{'M', 1},
};
for (const auto& [index, key, value] : std::views::enumerate(...
- 5,533
6
votes
1
answer
420
views
How does `template for` iteration work in C++26? [duplicate]
I'm experimenting with the new C++ compile-time reflection features (as described in P2996R0) and I testing a simple enum_to_string() utility using template for:
template <typename E>
requires ...
- 2,191
0
votes
3
answers
94
views
C++ - Range based loop and namespaces [duplicate]
I've read that to make one's custom container work with range-based for loop, "things" need to be in the same namespace. What things need to be in same namespace? The begin-end free ...
- 993
2
votes
1
answer
150
views
What would happen if I append elements in range based for? [duplicate]
I want to modify (push_back) element while iterate vector like this:
auto main() -> int {
std::vector<double> v { 1, 2, 3 };
for (auto& num : v) {
std::cout << num &...
- 65
2
votes
2
answers
118
views
get lines from a ifstream into strings in a range-based for loop
I use to parse lines from a file by writing,
ifstream input(filename);
for (string line; getline(input, line); /**/)
do_something_with(line);
...
but is it possible to elegantly (or with some boost ...
- 489
1
vote
1
answer
236
views
C++ Does Ranged-Based For Loop Use RValue Reference? [duplicate]
Hi I have a quick question - over here it says ranged-based for loops of the form
for ( init-statement (optional) range-declaration : range-expression )
are equivalent to the code:
{
auto &&...
- 569
0
votes
1
answer
132
views
C++ Qt best way to loop over a vector that is a member of a vector of parent dummy objects also being looped over
I want to loop over a vector of objects each containing another vector of objects to be looped over in turn. The subvector/contained vector object members need to be able to be able to be modified and ...
- 569
0
votes
2
answers
175
views
Range of enums in C++
I'm confused with range of enums.
I have code like this:
namespace regs {
enum Control_0 {
THING1,
THING2,
THING3
};
enum Control_1 {
THING100,
THING200,
THING300
};
const auto ...
- 3
3
votes
1
answer
144
views
Range-based for loop: why is ordinary lookup not performed?
In range-based for when begin-expr and end-expr are begin(range) and end(range), the names begin and end are not looked up using ordinary lookup. Just ADL is performed. See C++23 [stmt.ranged]#1.3.3.
...
- 3,497
3
votes
2
answers
930
views
Erasing nodes of a std::map within a range-based "for" loop
I need to check data of a std::map, and remove some of them.
I'm using a range-based "for" loop, like this:
std::map<int, string> data { { 1, "name1" }, { 2, "name2"...
- 2,165
3
votes
2
answers
249
views
A c++20 range adaptor whose produced values are iterators to the underlying range
I want to have the following work
std::vector<int> range{0,1,2,3};
for(std::vector<int>::iterator vit : range | iterator_range ){
int v = *vit;
}
this would be equivalent to the ...
- 32.5k
0
votes
0
answers
47
views
range - based loop traversal in array [duplicate]
**The code I tried to implement is : **
#include<iostream>
using namespace std;
int main()
{
int n, k;
cout << "Enter the number of elements: \n";
cin >> n;
...
- 19
0
votes
1
answer
119
views
Why is iterating over the set and modifying element not allowed here [duplicate]
In the following code, we cannot iterate over set s1 using non-const reference. Why?
#include <set>
struct st {
unsigned int f;
std::set<int> s2;
};
struct comp {
bool operator()(...
- 439
0
votes
2
answers
133
views
Usage of std::span with non-iterable type
I was trying out some C++20 when I stumbled upon a rather strange (at least to me) situation. I was expecting the following code to not work with one of my examples (I've specified the expected ...
