元组向量和initializer_list [英] tuple vector and initializer_list

问题描述

我尝试使用gcc4.7编译以下代码段

I tried to compile the following snippets with gcc4.7

vector<pair<int,char> > vp = {{1,'a'},{2,'b'}};
//For pair vector, it works like a charm.

vector<tuple<int,double,char> > vt = {{1,0.1,'a'},{2,4.2,'b'}};

但是，对于元组向量，编译器会抱怨：

However, for the vector of tuples, the compiler complains:

错误：从初始值设定项列表转换为'std :: tuple'将使用显式构造函数'constexpr std :: tuple< > :: tuple（_UElements&& ...）[with _UElements = {int，double，char}; =无效； _Elements = {int，double，char}]'

error: converting to ‘std::tuple’ from initializer list would use explicit constructor ‘constexpr std::tuple< >::tuple(_UElements&& ...) [with _UElements = {int, double, char}; = void; _Elements = {int, double, char}]’

编译器溢出的错误信息对我来说完全是乱码，我不知道元组的构造函数是如何实现的，但是我确实知道使用统一初始化完全可以（例如： tuple< int，float，char> {1,2.2，'X'} ），因此，我想知道我遇到的问题仅仅是编译器的TODO还是C ++ 11标准定义的问题。

The error info spilled by the compiler is total gibberish for me, and I have no idea how were the constructors of tuple implemented, yet I do know they're totally okay with uniform initialization (like: tuple<int,float,char>{1,2.2,'X'}), therefore, I wonder if the problem I encountered is only a TODO of the compiler or it's something defined by the C++11 standard.

推荐答案

相关的 std :: tuple 构造函数为 explicit 。这意味着您想做的事是不可能的，因为要使用的语法是根据复制初始化定义的（禁止调用 explicit 构造函数）。相反， std :: tuple< int，float，char> {1，2.2，'X'} 使用直接初始化。 std :: pair 确实只有非 explicit 构造函数。

The relevant std::tuple constructors are explicit. This means that what you want to do is not possible, since the syntax you want to use is defined in terms of copy initialization (which forbids calling an explicit constructor). In contrast, std::tuple<int, float, char> { 1, 2.2, 'X' } uses direct initialization. std::pair does have non-explicit constructors only.

使用直接初始化或使用标准元组工厂函数之一（例如 std :: make_tuple ）。

Either use direct-initialization or one of the Standard tuple factory function (e.g. std::make_tuple).

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