56,759 questions
-4
votes
0
answers
123
views
C++ Vector and type of Class [closed]
Hello all @ stack overflow
i have a question
vector<SSDS> abc(10);
abc[0].insert_in(1,"Sandisk","1","2","3");
abc[1].insert_in(2,"Western&...
2
votes
1
answer
186
views
Are the iterators of `map<key, value, greater<>>` and `map<key, value, less<>>` guaranteed to be the same type?
I have 2 maps
using BidBook = std::map<float, int, std::greater<>>; // price -> qty
using AskBook = std::map<float, int, std::less<>>;
I have a struct that contain iterator ...
- 1,989
16
votes
2
answers
718
views
Parsing of small floats with std::istream
I have a program that reads the coordinates of some points from a text file using std::istringstream, and then it verifies the correctness of parsing by calling stream's operator bool().
In general it ...
- 24.7k
1
vote
1
answer
140
views
Are the map/multimap iterators interchangeable?
In the code below I'm defining a map and a multimap. Then I'm defining four iterators assigning them values from these containers:
std::map<int, double> m;
std::multimap<int, double> mm;
...
- 6,650
0
votes
0
answers
65
views
Commands out of sync MySQL error - possible missing commit [duplicate]
I'm trying to run:
BEGIN TRANSACTION;
CREATE TABLE IF NOT EXIST abc();
SELECT( IF( ( SELECT 1 FROM information_schema.statistics WHERE index_name = 'abc_x' AND table_name = 'abc' ) > 0, SELECT 0, ...
- 6,473
15
votes
4
answers
1k
views
What is the size of std::array<T,0>?
Unlike C array, std::array is allowed to have zero length. But the current implementations differ in how std::array<T,0> is implemented, in particular the sizes of the object are different.
This ...
- 24.7k
3
votes
1
answer
321
views
How strong is the as-if rule in C++
As an exercice and side project I have started to write a runtime SIMD library in C++ that wraps around the intrinsics and that builds an expression tree. Each possible node in a tree must contain an ...
- 133
0
votes
1
answer
104
views
Undefined reference to header only library [duplicate]
Goal
Use concise makefile with organized directory structure. In particular, I don't want to have to edit the makefile to manage dependencies with every new source addition. The assumed directory ...
- 115
6
votes
2
answers
209
views
C++ pointers and concurrency
I need some help for understanding general basics of shared resource access in C++ multithreading.
When I need some variable that must be accessible for several threads, I declare it as atomic, or ...
8
votes
2
answers
332
views
When creating a C style header, is it ABI compatible to switch between enum and enum class?
I'm creating a dll + supporting header for a C library; which then has a C++ implementation.
The header file exposes an enum, returned by some of the functions.
Is this example guaranteed to produce ...
- 7,165
8
votes
2
answers
346
views
Move constructor called with copy elision?
The following code prints "move constructor" with c++11/c++14 with -fno-elide-constructors. However, with c++17/c++20 and -fno-elide-constructors, no "move constructor" prints.
Why ...
- 343
1
vote
1
answer
128
views
Correct way to set ready flag for std::condition_variable [duplicate]
I have two threads where one thread needs to wait for the other thread to complete its task. To solve this problem I decided to use std::condition_variable.
My question is, should the thread that is ...
- 1,349
1
vote
1
answer
169
views
Why is it impossible to cast ref-unqualified member function pointer to a ref-qualified member function pointer?
This code is rejected by all compilers I could test it on, so I suppose it is ill-formed according to the standard.
struct X {
void f();
};
void (X::*fptr)() & = &X::f; // ERROR
Here we ...
- 499
2
votes
2
answers
125
views
How to partially specialize for a type nested in a template?
I have a template struct with a nested class, eg.
template <typename T>
struct example {
struct type { };
};
template <typename T>
using example_t = typename example<T>::type;
...
- 3,753
-1
votes
2
answers
127
views
Reinterpret_cast array of bits as byte [closed]
I want to cast an array of bits into a byte, it works by using a loop and bitshift, but I think it would be cost inefective if run repeatedly (I might be wrong). So I wanted to use a pointer with ...
- 41