Recent questions tagged C++

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By trying to solve this problem, something made me wonder. Consider the following code: template <typename T> ... widespread? Is this standard? 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++ - FAQ: Why does dynamic_cast only work if a class has at least 1 virtual method?

This does not compile in C++: class A { }; class B : public A { }; ... A *a = new B(); B *b = dynamic_cast<B*>(a); 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++ - 'Inaccessible direct base' caused by multiple inheritance

Spoiler alert: Maybe a stupid question. :) #include <iostream> using namespace std; class Base { public: virtual ... come from? In constructor? 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 do I redirect output to a file with CreateProcess?

I tried using CreateProcess to run a simple command like hg > test.txt. I tried running the string as a whole (as ... .txt", ...) does not? 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++ - Passing a variable as a template argument

I am working with a library which exposes an interface to work with. One of the functions of this library is like ... . How can I do that? 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++ - cannot convert 'std::basic_string<char>' to 'const char*' for argument '1' to 'int system(const char*)'

I get this error: "invalid operands of types 'const char*' and 'const char [6]' to binary 'operator+'" when i ... filename '"+name+".jpg'"); 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 a template function in a template argument list

Suppose I have a template function: template<typename T> T produce_5_function() { return T(5); } How can I pass ... is "you cannot do 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++ - Does this really break strict-aliasing rules?

When I compile this sample code using g++, I get this warning: warning: dereferencing type-punned pointer will ... 't actually alias any type? 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 is the proper use of the comma operator?

I saw this code: if (cond) { perror("an error occurred"), exit(1); } Why would you do that? Why not just: ... ("an error occurred"); exit(1); } 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++ - scope of using declaration within a namespace

Is it safe (and correct) in a C++ header file to use the using declaration within a namespace as follows ... any file that includes this header? 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++ - Is std::vector memory freed upon a clear?

Suppose I have a std::vector of structs. What happens to the memory if the vector is clear()'d? std:: ... vecs variable as a reusable buffer? 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 declare constexpr extern?

Is it possible to declare a variable extern constexpr and define it in another file? I tried it but the compiler ... : constexpr int i = 10; 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++ - launch an exe/process with stdin stdout and stderr?

With C++ how do i launch an exe/process with stdin stdout and stderr? I know how to do this in .NET and ... for the same project in the future. 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++ - Order of execution in constructor initialization list

Is order of execution in constructor initialization list determinable? I know that members order in a class is the ... line into the body. See Question&Answers more detail:os...

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

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238 views

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c++ - Calculating size of an array

I am using the following macro for calculating size of an array: #define G_N_ELEMENTS(arr) ((sizeof(arr))/(sizeof( ... : bffffa40 sizeof arr: 1 See Question&Answers more detail:os...

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

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178 views

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c++ - Virtual tables and memory layout in multiple virtual inheritance

Consider following hierarchy: struct A { int a; A() { f(0); } A(int i) { f(i); } virtual void f(int i) ... 3); Why all the calls to f print 33? 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++ - Is a constexpr array necessarily odr-used when subscripted?

Given the following code: struct A { static constexpr int a[3] = {1,2,3}; }; int main () { int a ... endless version of a debate in the Lounge. See Question&Answers more detail:os...

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

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264 views

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c++ - overloaded functions are hidden in derived class

In a derived class If I redefine/overload a function name from a Base class, then those overloaded functions are not ... f() and f(string). 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++ - Use WM_COPYDATA to send data between processes

I wish to send text between processes. I have found lots of examples of this but none that I can get ... trying to avoid MFC and dependencies. 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 is modifying a string through a retrieved pointer to its data not allowed?

In C++11, the characters of a std::string have to be stored contiguously, as § 21.4.1/5 points out: ... GetTextLength()); GetText(text.data()); See Question&Answers more detail:os...

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

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215 views

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c++ - Do I have to use #include <string> beside <iostream>?

I started learning C++ and I read a book which writes that I must use the <string> header file because the ... ? Why? Is there some difference? See Question&Answers more detail:os...

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

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309 views

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c++ - Why are some functions in <cmath> not in the std namespace?

I am developing a project which works with multiple arithmetic types. So I made a header, where the minimal ... did I misunderstand something? 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 pointer value

I am trying to declare a constexpr pointer initialized to some constant integer value, but clang is foiling all my ... gcc accepts all of these. 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 std::map operator[] create an object if the key doesn't exist?

I'm pretty sure I already saw this question somewhere (comp.lang.c++? Google doesn't seem to find it there ... What benefit do it give? Thanks 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 do I return a char array from a function?

I've tried the following: char[10] testfunc() { char[10] str; return str; } See Question&Answers more detail:os...

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

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269 views

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c++ - Near and Far pointers

What is difference between our usual pointers(ones which we normally use), near pointers and far pointers and is ... will be very helpful. See Question&Answers more detail:os...

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

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636 views

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c++ - Compilation error: "stddef.h: No such file or directory"

Whenever I try to compile this code it always ends up with this error: In file included from /usr/include/wchar.h:6: ... World! :D"; return 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++ - The behaviour of floating point division by zero

Consider #include <iostream> int main() { double a = 1.0 / 0; double b = -1.0 / 0; double ... -eating, demon-sneezing undefined behaviour here. See Question&Answers more detail:os...

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

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