长双字面量的 C++ 后缀是什么？
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What's the C++ suffix for long double literals?
提问by Walter
In C++ (and C), a floating point literal without suffix defaults to double, while the suffix fimplies a float. But what is the suffix to get a long double?
在 C++（和 C）中，没有后缀的浮点文字默认为double，而后缀f意味着float. 但是得到 a 的后缀是long double什么？
Without knowing, I would define, say,
在不知道的情况下，我会定义，说，
const long double x = 3.14159265358979323846264338328;
But my worry is that the variable xcontains fewer significant bits of 3.14159265358979323846264338328than 64, because this is a doubleliteral. Is this worry justified?
但我担心变量x包含的有效位3.14159265358979323846264338328少于 64，因为这是一个double文字。这种担心有道理吗？
回答by Vlad from Moscow
From the C++ Standard
来自 C++ 标准
The type of a floating literal is double unless explicitly specified by a suffix. The suffixes f and F specify float, the suffixes l and L specify long double.
除非后缀明确指定，否则浮动文字的类型是 double 。后缀 f 和 F 指定 float，后缀 l 和 L 指定 long double。
It is interesting to compare with corresponding paragraph of the C Standard. In C there is used term floating constantinstead of floating literalin C++:
与 C 标准的相应段落进行比较是很有趣的。在 C 中使用术语 floating constant而不是floating literal在 C++ 中：
4 An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has type float. If suffixed by the letter l or L, it has type long double
4 无后缀的浮点常量具有 double 类型。如果以字母 f 或 F 为后缀，则它的类型为 float。如果以字母 l 或 L 为后缀，则类型为 long double
回答by Jens Gustedt
The C suffix is L. I'd strongly suspect that it is the same for C++.
C 后缀是L. 我强烈怀疑 C++ 也是如此。
Your worry is justified. Your literal would first be converted to a double, and thus truncated, and then converted back to long double.
你的担心是有道理的。您的文字将首先转换为 a double，从而被截断，然后转换回long double.
回答by Ivaylo Strandjev
Your concern is valid and you should use a Lsuffix for long double literal.
您的担忧是有效的，您应该L为 long double 文字使用后缀。
