Recent questions tagged C++

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c++ - The C `clock()` function just returns a zero

The C clock() function just returns me a zero. I tried using different types, with no improvement... Is this a ... , RedHat Linux, gcc 3.4.6 See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - using C function from other package in Rcpp

I'm trying to call a C routine from the cubature package in a c++ function to perform multidimensional ... using an external C function. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Thread safety of std::map for read-only operations

I have a std::map that I use to map values (field ID's) to a human readable string. This map is ... : Edited code sample for const correctness. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why does a push_back on an std::list change a reverse iterator initialized with rbegin?

According to some STL documentation I found, inserting or deleting elements in an std::list does not invalidate iterators. ... I'm not aware of? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Command working in terminal, but not via QProcess

ifconfig | grep 'inet' is working when executed via terminal. But not via QProcess My sample code is QProcess p1; p1 ... I tried that as well:( See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Uses for negative zero floating point value?

Consider the following C++ code: double someZero = 0; std::cout << 0 - someZero << ' '; // prints 0 ... of smacking a minus onto a variable)? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to know if a type is a specialization of std::vector?

I've been on this problem all morning with no result whatsoever. Basically, I need a simple metaprogramming thing that ... such a thing exist ? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - constexpr function parameters as template arguments

I am playing around with some toy code using c++11 to figure out a bit more about how things work. ... should be available at compile time. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to ensure that the template parameter is a subtype of a desired type?

I have a template class, what I want to do are the following Make sure that an object is instantiated only if the ... up my C++ learning rate. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Converting epoch time to "real" date/time

What I want to do is convert an epoch time (seconds since midnight 1/1/1970) to "real" time (m/d/y h:m ... there is a "better" solution to this. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - how to restart my own qt application?

i just asking myself how to restart my own qt application? Can somebody please show me an example? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to call derived class method from base class pointer?

I have a class structure similar to the following class A { public: A(void); ~A(void); void DoSomething(int i ... derived class to cast it to? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Where in Qt Creator do I pass arguments to a compiler?

Where in Qt Creator do I pass arguments to a compiler? It isn't really that obvious. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - std::map default value for build-in type

Recently, I was confused by the std::map operator[] function. In the MSDN library, it says: "If the argument ... is construted with the value 0. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - structured binding with [[maybe_unused]]

Functional languages with pattern matching (sometimes?) have the possibility to ignore some bound values, but with C ... .godbolt.org/z/H2duYd See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Training custom SVM to use with HOGDescriptor in OpenCV

I'm trying to train my own detector for use with OpenCV::HOGDescriptor but I'm having trouble making the ... me in the right direction? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Finding nearest point in an efficient way

I've got a point in 2d plane for example (x0,y0) and a set of n points (x1,y1)...(xn,yn) and I want to find ... x<b.x; else return a.y<b.y; } See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Capturing a time in milliseconds

The following piece of code is used to print the time in the logs: #define PRINTTIME() struct tm * tmptime; ... way to add milliseconds to this? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What are good practices regarding shared libraries on Linux?

I recently read a lot about shared libraries on Linux, and here is what I learnt: A shared library should embed ... packaged). Is this correct ? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Multiple implicit conversions on custom types not allowed?

class C { public: C() { } }; class B { public: B(C c) { } B() { } }; class A ... is the general rule describing multistep implicit conversion? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - How to pass command line arguments to a c program

I've known how to write a program that accepts command line arguments ever since I learned to program. What I don' ... sort of a novice at this. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Read file names from a directory

I was wondering if there's an easy way in C++ to read a number of file names from a folder containing many ... be done using simple C++ methods. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why not to inherit from std::allocator

I created my own allocator like so: template<typename T> class BasicAllocator { public: typedef size_t size_type; typedef ... to do that? Why? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - What do I need to do before deleting elements in a vector of pointers to dynamically allocated objects?

I have a vector that I fill with pointers to objects. I am trying to learn good memory management, and have a ... vector to go out of scope)? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Why doesn't delete destroy anything?

I'm playing a little with memory dynamic allocation, but I don't get a point. When allocating some memory with the ... return 0; } Any clue ? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - effective way to select last parameter of variadic template

I know how to select first parameter of variadic template: template< class...Args> struct select_first; ... parameter of variadic templates? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Does constraint subsumption only apply to concepts?

Consider this example: template <typename T> inline constexpr bool C1 = true; template <typename T> inline constexpr bool ... <T> subsume C1<T>? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Difference between 'strcpy' and 'strcpy_s'?

When i tries to use strcpy to copy a string it gave me a compile error. error C4996 'strcpy': This ... difference between strcpy and strcpy_s? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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