问题描述
以下C ++无效，因为引用变量需要初始化程序：
The following C++ is invalid because reference variables require initializers:
int& a; // illegal
if (isfive) {
a = 5;
} else {
a = 4;
}
但是，MSVC似乎认为这还可以：
However, MSVC seems to think this is okay:
int& a = isfive ? 5 : 4;
对我而言，这意味着MSVC实际上将条件运算符视为单个表达式，而没有将其扩展为
This implies to me that MSVC is actually treating the conditional operator like a single expression and not expanding it into an if-else statement.
使用条件运算符初始化引用始终是有效的C ++吗？
Is it always valid C++ to initialize a reference using the conditional operator?
推荐答案
MSVC具有非标准的扩展名。这意味着它允许破坏代码。
MSVC has a non-standard "extension". What it means is that it allows broken code. There's a good reason this is prohibited.
还请注意
int& a = 5;
在标准C ++中也不合法。
is not legal in Standard C++ either.
但是，通常，使用任何可以转换为正确类型（包括使用条件运算符）的表达式初始化 const 引用是合法的。用合法类型的左值初始化非 const 引用是合法的，条件运算符在某些条件下会产生该值。
In general, though, it is legal to initialize a const reference with any expression which can be converted to the right type (including use of the conditional operator). And it is legal to initialize a non-const reference with an lvalue of the right type, which the conditional operator yields under certain conditions.
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