Question

在Swift编程语言官方文档中，

Double represents a 64-bit floating-point number.
Float represents a 32-bit floating-point number.

链接：https://docs.swift.org/swift-book/LanguageGuide/TheBasics.html#ID321

然后，为什么会有Float64？它们之间有什么区别？还是一样？

Answer 1

转到Float64的定义

/// A 64-bit floating point type.
public typealias Float64 = Double

/// A 32-bit floating point type.
public typealias Float32 = Float

Answer 2

通过点击命令 + shift + o 并搜索Float64可以找到标题，例如：

/// A 64-bit floating point type.
public typealias Float64 = Double
/// A 32-bit floating point type.
public typealias Float32 = Float

和

Base floating point types 

    Float32         32 bit IEEE float:  1 sign bit, 8 exponent bits, 23 fraction bits
    Float64         64 bit IEEE float:  1 sign bit, 11 exponent bits, 52 fraction bits  
    Float80         80 bit MacOS float: 1 sign bit, 15 exponent bits, 1 integer bit, 63 fraction bits
    Float96         96 bit 68881 float: 1 sign bit, 15 exponent bits, 16 pad bits, 1 integer bit, 63 fraction bits

Note: These are fixed size floating point types, useful when writing a floating
      point value to disk.  If your compiler does not support a particular size 
      float, a struct is used instead.
      Use of of the NCEG types (e.g. double_t) or an ANSI C type (e.g. double) if
      you want a floating point representation that is natural for any given
      compiler, but might be a different size on different compilers.

通常，除非您要编写依赖于二进制表示形式的代码，否则应使用标准的Float v Double名称。但是，如果您在编写需要二进制兼容性的内容（例如，编写/解析二进制Data与其他平台进行交换），则可以使用名称中带有位数的数据类型，例如Float32与Float64对比Float80。

Double和Float64之间的快速区别

2 个答案: