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Questions tagged [constexpr]

constexpr is a modifier introduced in C++11, which informs the compiler that the value of a function or variable is known or can be calculated at compile time. As such, it can be used as a constant in places where otherwise it couldn't be.

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constexpr modifier has no effect

I have some problem with constexpr functions. I thought, any function declared with constexpr modifier must return compile-time constant, but actually it doesn't work. (Eclipse + MinGW, gcc 4.8.1) #include #include…
alphashooter
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Switch case statement with member variable in case

I am trying to find a way to evaluate a switch-case statement using a member variable in the case part. I thought that having a global static variable like below would be allowed as const-expression. Unfortunately the compiler tells me the…
Abruzzo Forte e Gentile
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constexpr won't work using Visual C++ Compiler Nov 2013 CTP (CTP_Nov2013)

I'm trying to implement a compile-time hash algorithm using constexpr. I Downloaded Nov 2013 CTP because it has supported for constexpr but thats a lie... #define hashCharacter(T, J) (((T >> 0x0D) | (T << 0x13)) + J) unsigned long constexpr…
Agustin Alvarez
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constexpr constructor with compile time validation

I'd like to build up a class with the option of constexpr-ness. And, of course, I'd like to take advantage of compile time error check. Every constexpr function, constructor included, must work also at runtime, when the given parameters are not…
nyarlathotep108
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link error while compiling this "simple" program with clang and g++

I am working on a project, and it seems that clang is unable to generate a valid bytecode (as the linker fail to link, some static constexpr in a template class is not found at link time) I can fix it with a static getter in the class, but this lead…
neam
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constexpression subscript operator of STL containers

constexpr const_reference at( size_type pos ) const; How can this overload of STL container accessors work with non-constexpr parameters? What are classical use cases of this overload?
Meteorhead
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const double expression in C++

in the English Wikipedia page on C++11, we can read that: Prior to C++11, the values of variables could be used in constant expressions only if the variables are declared const, have an initializer which is a constant expression, and are of…
Greg82
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profiling constexpr with const char array parameters shows run-time execution

I do a lot of hashing in a program of mine, so I decided to hack up a constexpr function that can do at least some of the hashing for me at compile-time. After successfully implementing a constexpr hash function, I profiled the code and it is…
Brandon
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C++ Declare array whose size value from const array

I'm trying to define a stack c-style array whose size is taken from const array and is known in compile-time. const int size[2]={100, 100}; int ar[size[0]]; //error: expression must have a constant value It fails. How it can be fixed?
Mark Kahn
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how can I create a template from string literal?

I want to create a template class from string literal: create_eq("abcdefg") get IEqual<'a','b','c','d','e'> but ISO C++11's User-defined literals only support integer-literal and floating-literal : template IEqual …
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constexpr-izing the jesteress hashing algorithm

After some head-scratching, I've managed to constexpr-ize the Jesteress hashing algorithm. The compiler, however, refuses to generate a constant out of a cjesteress() call, such as in std::cout << cjesteress("test) << std::endl;, but generates code…
user1095108
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Why using constant expression as a template parameter?

When it is better to have a private data member (_val in class B) and when it is better to have val as a template parameter (class A)? #include using namespace std; template class A{ public: A(){ cout << val <<…
cpp
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Compiler error when using constexpr and lambda

I encountered a problem when using constexpr functions together with lambdas. The following code is a minimal version which reproduces the error: #include constexpr unsigned bar(unsigned q) { return q; } template
Danvil
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Variadic template doesn't recognise a constexpr function

I'm trying to initialize some C++ array at compile time but I got a weird g++ error. Here is the smallest chunk of code I've been able to get which reproduce the error: #include template constexpr Ar Map(typename…
hivert
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Literals and constexpr functions, compile-time evaluation

Attempting to implement a pleasing (simple, straightforward, no TMP, no macros, no unreadable convoluted code, no weird syntax when using it) compile-time hash via user-defined literals, I found that apparently GCC's understanding of what's a…
Damon
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