西瓜皮儿

String

2023/1/27

# 基础使用

  • 其他操作无法隐式转换
    let label = "The width is "
let width = 94

//let widthLabel = label + width // 报错

let widthLabel = label + String(width) 正确

 print(widthLabel)
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  • 换行String
    let apples = 3
let oranges = 5
let q = """
I said "我有 \(apples) 个苹果"
我有 \(apples + oranges) 个水果"
"""

print(q)
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  • 通过数组初始化
    let catCharacters: [Character] = ["C", "a", "t", "!", "🐱"]
let catString = String(catCharacters)
print(catString) // Cat!🐱
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# 获取字符串

# for...in遍历

let s = "Hello, World!"

for i in s {
    print(i)
}
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# 下标遍历

  • 正向遍历
    let a = "abcdefg";

for i in (0..<a.count) {
    let char = a[a.index(a.startIndex, offsetBy: i)]
    print(char) // a b c d e f g
}
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  • 反向遍历
    let a = "abcdefg";

for i in (0 ..< a.count).reversed() {
    let char = a[a.index(a.startIndex, offsetBy: i)];
    print(char); // g f e d  c b a
}
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# count

  • 长度
let s = "abcdefg";
print(s.count); // 7
let c = s.1;
print(c);
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# 下标

var a = "abcdefg";

// 第三位访问，下标是2
let b = a[a.index(a.startIndex, offsetBy: 2)] // 2就是下标
print(b); // c

// 最后一位访问
let c = a[a.index(before: a.endIndex)]
print(c); // g

// 第一位访问
let d = a[a.startIndex]
print(d); // a

// 倒数第三位访问
let f = a[a.index(a.endIndex, offsetBy: -3)]
print(f); // e
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# 区间

  • 拿到3 ～ 5的区间（按照下标的原理，是下标3 ～ 下标5）
    var me = "你好呀我是西瓜皮儿"

print(me[me.index(me.startIndex, offsetBy: 3)...me.index(me.startIndex, offsetBy: 5)]) // 我是西
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  • 拿到0 ～ -2位区间
    let a = "abcdefg";

let start = a.startIndex;
let end = a.index(a.endIndex, offsetBy: -2);

print(a[start ... end]); // abcdef
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# indices

  • 获取字符串的整体索引范围range
var a = "abcdefg";

for idx in a.indices {
    let b = a[idx]
    print(b) // a b c d e f g
}
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# 增删改查

# 拼接

  • 拼接，两种方法
    • 【+】号只能做字符串类型的拼接
    • 【\ ()】可以拼接任意类型

+号

var me = "123"
me += "4"
print(me) // 1234
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【\ ()】

let apples = 3
let oranges = 5

let fruitSummary = "我有 \(apples + oranges) 个水果."

print(fruitSummary); // 我有 8 个水果.
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# append

var me = "123"
me.append("4")
print(me) // 1234
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# firstIndex

  • 拿到第一个需求字符的index，类型是Index
  • 只接收单个字符
var me = "你好呀我是西瓜皮儿"

let firstYa = me.firstIndex(of: "呀")

print(firstYa) // Optional(Swift.String.Index(_rawBits: 393985))

print(me[firstYa!]) // 呀
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# lastIndex

  • 拿到倒数第一个需求字符的index，类型是Index
  • 只接收单个字符
var me = "你好呀我是西瓜皮儿呀"

let firstYa = me.lastIndex(of: "嘿")

if let firstYa {
    print(me[firstYa]) // 呀
}
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# insert

注：修改原字符串

  • 插入单个字符
    var s = "abcdefg";
s.insert("h", at: s.endIndex)
print(s) // abcdefgh
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  • 插入多个字符
    var s = "abcdefg";
s.insert(contentsOf: "hhhh", at: s.endIndex)
print(s) // abcdefghhhh
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# contains / hasPrefix / hasSuffix

let s = "abcdefg";

// 单个包含
print(s.contains("g")); // true
print(s.contains("h")); // false

// 连续包含
print(s.contains("abc")); // true
print(s.contains("ac")); // false

// 分别包含
print(s.contains(where: String.contains("ac"))); // true

// 前缀
print(s.hasPrefix("abc")); // true
print(s.hasPrefix("ac")); // false

// 后缀
print(s.hasSuffix("fg")); // true
print(s.hasSuffix("f")); // false
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# remove

  • 注：会改变原字符串
var a = "abcdefg";

a.remove(at: a.index(a.startIndex, offsetBy: 2))
print(a) // abdefg
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# removeSubrange

var me = "你好呀我是西瓜皮儿呀"

me.removeSubrange(me.startIndex...me.index(me.startIndex, offsetBy: 3))

print(me); // 是西瓜皮儿呀
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# replaceSubrange

  • 下标替换
var a = "abcdefg";

a.replaceSubrange((a.startIndex ... a.index(a.endIndex, offsetBy: -2)), with: "xxxxxx");
print(a); // xxxxxxg
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# replacingOccurrences

  • 指定匹配替换（返回新String）
  • 全部替换
var me = "我说：你好呀我是西瓜皮儿呀"

let b = me.replacingOccurrences(of: "我", with: "小黄")

print(b) // 小黄说：你好呀小黄是西瓜皮儿呀
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# prefix

  • Substring 的实例：截取前固定位数的字符串，相当于从首字母获取固定长度区间

Swift 里的 Substring 绝大部分函数都跟 String 一样，意味着你可以使用同样的方式去操作 Substring 和 String。然而，跟 String 不同的是，你只有在短时间内需要操作字符串时，才会使用 Substring。当你 Substring占用了原String储存空间，

let s = "abcdefg";

print(s.prefix(3)); // abc

// 同
print(String(s[s.startIndex...s.index(s.startIndex, offsetBy: 2)])); // abc
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  • Substring转String
    var a = "abcdefg";

let b = a.prefix(a.count)

a.remove(at: a.startIndex)
print(a) // bcdefg
print(b) // abcdefg

let c = String(b);
print(c); // abcdefg
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# 其他操作

# lowercased

  • 转小写
var me = "Aksld3B"
let lowerMe = me.lowercased()
print(lowerMe) // aksld3b
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# uppercased

  • 转大写
    var me = "Aksld3B"
let upperMe = me.uppercased()
print(upperMe) // AKSLD3B
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  • 首字母大写
    var me = "aksld3B"

func upperFirstChar(_ s: String) -> String {
    var firstChar = String(s[s.startIndex])
    firstChar = firstChar.uppercased();
    var a = s;
    a.replaceSubrange(a.startIndex...a.startIndex, with: firstChar)
    return a;
}
let upperMe = upperFirstChar(me);
print(upperMe) // Aksld3B
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# isEmpty

  • 相对于 == ""，可以让代码更少字符串
    var a = "abcdefg";
var b = "";

print(a.isEmpty) // false
print(a == "") // false

print(b.isEmpty) // true
print(b == "") // true
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# 特殊解析

  • 【\ "】可以解析包含双引号
    var a = "\"abcdefg\"";

print(a); // "abcdefg"
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  • 【# "】可以不解析内部【\ ()】语法
    var name = "小黄"
var a = #"abcdefg\(name)"#;

print(a); // abcdefg\(name)
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上次更新: 9/17/2024

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