Question

我有一个从json服务器响应初始化的浮点数，例如65.788、43.77、89、58.86985… 我只需要用两位小数位打印即可。但是没有任何回合。

我的问题是，当我将浮点数格式化为仅添加两位数字时，这种格式将自动舍入最后一位数字。

let weight = 65.788
let string = String(format: "%.2f", weight). // ->  65.79

我得到65.79，但我需要得到65.78

如何从json响应数中仅取两位而不取整？谢谢！

Answer 1

将NumberFormatter与.roundingMode = .down

一起使用

    let nf = NumberFormatter()
    nf.roundingMode = .down

    // max of 2 decimal places (e.g. 1.23, 1.2, 1)
    nf.maximumFractionDigits = 2

    // starting with Strings
    ["65.788", "1.2", "1.9", "1"].forEach { s in
        let n = Float(s)
        let t = nf.string(for: n)
        print("[" + t! + "]")
    }

    // starting with Numbers
    [65.788, 1.2, 1.9, 1].forEach { n in
        let t = nf.string(for: n)
        print("[" + t! + "]")
    }

    // if you want exactly 2 decimal places (e.g. 1.23, 1.20, 1.00)
    nf.minimumFractionDigits = 2

    // starting with Strings
    ["65.788", "1.2", "1.9", "1"].forEach { s in
        let n = Float(s)
        let t = nf.string(for: n)
        print("[" + t! + "]")
    }

    // starting with Numbers
    [65.788, 1.2, 1.9, 1].forEach { n in
        let t = nf.string(for: n)
        print("[" + t! + "]")
    }

输出：

[65.78]
[1.2]
[1.9]
[1]
[65.78]
[1.2]
[1.9]
[1]
[65.78]
[1.20]
[1.90]
[1.00]
[65.78]
[1.20]
[1.90]
[1.00]

很显然，您想使用错误检查来确保将原始字符串转换为数字，等等。

Answer 2

我喜欢单行解决方案，这里有一个

let weight = 12.99999
let string = "\(Double(floor(weight * 100)/100))"
print(string) // 12.99

如何在Swift中仅四位数打印浮点数而不四舍五入？

2 个答案: