General C++ Programming - C++ Forum

An expression is potentially evaluated unless it is the operand of the sizeof, noexcept, typeid, decltype etc.. https://en.cppreference.com/w/cpp/language/ex...

[19 replies] Last: [quote=malibor] static_assert is a good trick to see if it's evaluate... (by Peter87)

by JUANDENT

parsing durations using %q or %Q??

cannot parse durations using %q or %Q...e.g. std::chrono::duration<long long, std::milli> dur{ 1200 }; std::istringstream sm{ "1000ms" }; auto str =...

[5 replies] Last: Maybe something like: #include <chrono> #include <iostream> #includ... (by seeplus)

by JUANDENT

parsing a formatted string

using the format library in C++20, and having done this: int val = 25; string str = std::format( "{0:2}", val); How can we get the val from str, somethin...

[6 replies] Last: To just obtain a number from std::string, there are the stoxxx functio... (by seeplus)

by JUANDENT

I don't understand ISO week

Please explain why Sunday jan 1, 2023 prints as 52 using %V -- why is that different to week 1? week 1 starts with Jan 1 for every year... Doesn't make...

[1 reply] : [quote=JUANDENT]week 1 starts with Jan 1 for every year... Nope. Eve... (by Peter87)

by JUANDENT

now() returns same as current_zone()->to_local(now())

Hi, system_clock::now() returns the same value as chr::current_zone()->to_local(now()); I expected now() to return UTC value and to->local(now()) to return CS...

[1 reply] : A quick search reveals: https://en.cppreference.com/w/cpp/chrono/utc_... (by TheIdeasMan)

by malibor

Should destructors be noexcept?

I'm working on a library which whose classes are almost all hierarchical, problem is that if upmost class destructor is declared noexcept then all destructors i...

[13 replies] Last: There is nothing in the C++ standard that demands that this should ge... (by malibor)

by shekharsahoo

Need Help to find the error

I have below code, for functor. But this is giving compilation error in VS17. #include <iostream> #include <functional> template <typename T> struct less...

[3 replies] Last: Now I understand, the problem. Yes thanks to both of you for the clari... (by shekharsahoo)

by JUANDENT

where can I find trim() in std C++?

I expected std::string to have a member function trim() but it does not. How to accomplish this??

[4 replies] Last: Using ranges, then possibly something like this which will trim white-... (by seeplus)

by JUANDENT

is this object dangling?

hi, I have this code assert(ltrim_copy(str) == "¢4,500.55"); // line 1 ltrim_copy returns a temporary object... is it ok to compare it with...

[1 reply] : it's OK and it is destroyed when assert returns. (by malibor)

by LukeProducts

Neuronal Network not working properly..

Dear Community, I'm wondering what I'm doing wrong when it comes to building neural networks and I can't come up with a solution on my own. I want to build a...

[4 replies] Last: You implementation is missing a "Neuron" class, "Layer" class, "Synaps... (by malibor)

by JUANDENT

how can a function name be an lvalue?

take this function: int abs(int a) { return a < 0 ? -a : a; } abs is supposed to be an lvalue but it cannot be assigned!! int xy(int);...

[8 replies] Last: [quote=seeplus]In my mind (and the language lawyers will probably squa... (by Peter87)

by Cplusc

blockMesh generator

Following my question regarding hexahedral mesh generation in a domain using the STL file representing the surface triangulation here https://cplusplus.com/foru...

[10 replies] Last: > Actually this is not a big code at all Big enough for you to dump on... (by salem c)

by seeplus

Age calculation

With C++20/23 std::chrono and a birthdate as either type sys_days or year_month_day, is there any 'easy' way to obtain their age as years, months and days. It's...

[1 reply] : We've come up with this: struct Age { unsigned years {}; unsigned... (by seeplus)

by Cplusc

Building project from github

I'm trying to build this project https://github.com/hemelb-codes/hemelb. This project has several dependencies. I have several of them installed in my system ...

[4 replies] Last: vcpkg is used with Visual Studio. step 1: install all deps with corre... (by malibor)

by malibor

Force implicit conversion of a string literal in templated class?

The code below doesn't compile because string literal instead of std::string is given to constructor. #include <string> #include <type_traits> template<typ...

[3 replies] Last: C++17! https://en.cppreference.com/w/cpp/language/class_template_argu... (by mbozzi)

by Cplusc

generate mesh inside .STL file

I have some STL files (usually aneurysm) and I'm using Lattice Boltzmann Method for my simulation and I need to construct the mesh. As far as LBM uses cubic mes...

[18 replies] Last: I would strongly appreciate any idea on my way of generating mesh insi... (by Cplusc)

by seeplus

year_month_day vs sys_days

When dealing with dates - year, month, day (not times) - either year_month_day or sys_days can be used. Is there guidance as when one or the other should be use...

[9 replies] Last: [quote=seeplus]When do you get 8 for sys_days? libstdc++ (64-bit) htt... (by Peter87)

by seeplus

Chrono date literals

Since C++20 there has been the d and y literals defined in <chrono> - but no m. This seems to be able to be added by (for VS - based upon the code for d and ...

[4 replies] Last: I get forward thinking & future planning, but c++ has no business stan... (by jonnin)

by JUANDENT

How can I find the maximium number of decimal digits representable in a double?

What is the maximum precision of double? numeric_limits<double>::????? default precision is 6 digits after the period

[3 replies] Last: https://en.cppreference.com/w/cpp/types/numeric_limits/digits10 (by Peter87)

by allenmaki

output will show only the end.

Hello everybody. I really thank you for helping me to go back to programming in C++. You know I am now 73 years old. They told me I have to stay busy to sta...

[6 replies] Last: What exactly do you want to know? Let's say your terminal/cmd has 100 ... (by Ganado)

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General C++ Programming - March 2023