Recent questions tagged c++

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c++ - Range TS idioms and the mysterious auto &&

In pre-Range TS code, I might do something like the following to get a (potentially modifiable) reference ... reference to capture it? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - default template class argument confuses g++?

Yesterday I ran into a g++ (3.4.6) compiler problem for code that I have been compiling without a problem using the ... = Foo<int,int>() ); See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Is `new (this) MyClass();` undefined behaviour after directly calling the destructor?

In this question of mine, @DeadMG says that reinitializing a class through the this pointer is undefined ... once for every constructor. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Must construct a QApplication before a QWidget & Invalid parameter passed to C runtime function

I finished migrating an application from Qt4 to Qt5, it compiles and everything but it crashes at a certain ... constructor but I cant. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - QWidget::heightForWidth() is not called

I want to make my widget always have square size. Following this answer, I have overridden QWidget::heightForWidth( ... on Linux and Windows. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Deduction guide and variadic templates

Consider the following code: #include <tuple> #include <iostream> template <class T> struct custom_wrapper { template ... that a compiler bug? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Passing template function as argument for normal function

I'm wondering if it's possible to pass a template function (or other) as an argument to a second function ( ... to be defined for execute() ? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What's the purpose of dummy addition in this "number of elements" macro?

Visual C++ 10 is shipped with stdlib.h that among other things contains this gem: template <typename _CountofType ... problem does it solve? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - fallocate vs posix_fallocate

I am debating which function to use between posix_fallocate and fallocate. posix_fallocate writes a file right away ( ... Thanks for your time. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - C2070 - illegal sizeof operand

The following code looks fine to me: #include <stdio.h> template <typename T> struct A { static float m_kA[]; ... array to be a template. Thanks See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why must I use address-of operator to get a pointer to a member function?

struct A { void f() {} }; void f() {} int main() { auto p1 = &f; // ok auto p2 = f; // ... -of operator to get a pointer to a member function? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Is there any built-in function that convert wstring or wchar_t* to UTF-8 in Linux?

I want to convert wstring to UTF-8 Encoding, but I want to use built-in functions of Linux. Is there any built ... ](str); // Simple invoke. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What is the Windows equivalent of the Unix function gmtime_r?

I am porting some Unix code into Windows Visual Studio 2010. I have run into the following line gmtime_r(&now, ... me in the right direction? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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367 views

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c++ - Use decltype and std::function with lambda

This works ... auto x = 4; typedef decltype(x) x_t; x_t y = 5; ... so why doesn't this? ... I declare lambda_t manually using std::function? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What's are practical example where acquire release memory order differs from sequential consistency?

Clearly, sequential consistent atomic operations differ in their valid observable behavior from acquire-release ... sequential consistency. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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176 views

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c++ - Disabling C++0x features in VC 2010?

Does C++0x mode in VC++ 2010 has an off switch? I am working on a project that supposed to compile on ... Language Extensions but that's not it. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Is std::ofstream movable?

I have this map which compiles fine in MSVC10 : std::map<std::string, std::ofstream> m_logFiles; But on ... use of b deleted copy constructor. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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276 views

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c++ - Regex Boost library linking in release mode warns "duplicate section has different size" when using mingw-w64 toolchain

When linking my project in the release mode I am getting the following warning: myProject-libs/release/libboost_regex ... the linked question). See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - false implicitly convert to null pointer

Whether false is allowed to be implicitly converted to pointer is different between clang++ and g++: g++-4.8: ... ^~~~~ 1 error generated. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Understand structured binding in C++17 by analogy

I'm trying to understand structured binding introduced in C++17. The explanation on cppreference is not obvious to ... analogy failed to catch? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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537 views

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c++ - Saving an image with imwrite in opencv writes all black but imshow shows correctly

Original Question This example code will display the image created correctly, but will save a png with only black pixels. ... (0); return 0; } See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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592 views

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c++ - what is the best way to avoid negative zero in output?

As in this question is said, there is some differences between negative and positive zero in floating point numbers. I ... * -1 will not work. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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390 views

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c++ - Divide by zero prevention

What is 1.#INF and why does casting to a float or double prevent a division by 0 of crashing? Also, any great ... < endl; //Output = 1.#INF See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - 'default' as a variable name

While debugging some code, I came across an array named default. I thought that keywords were not allowed as ... a property with this name! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - GCC warning about implicit dereference

I just ran across the following warning in GCC: warning: implicit dereference will not access object of type volatile ... }; Any ideas? Thanks! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why does Qt use a signed integer type for its container classes?

The question is clear. I wonder why they even thought this would be handy, as clearly negative indices are ... design for some reason... See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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186 views

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c++ - Comparing command parameter with argv[] is not working

I am trying to compare the parameter of command with argv[] but it's not working. Here is my code. ./a ... why this comparison is not working. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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198 views

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c++ - Why 10^1 is 11?

I am currently learning C++. I was trying to compute power of an integer using the expression: val=10^1; ... is giving me the wrong result. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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