go語言怎麼比較字串

<blockquote><p>比較方法：1、直接使用“==”運算子比較，語法“str1 == str2”，該方法區分大小寫。 2.利用strings套件的Compare()函數比較，語法「strings.Compare(a,b)」；傳回值為int型別，0表示兩數相等，1表示a大於b，「-1」表示a小於b 。 3.利用strings套件的EqualFold()比較，語法「strings.EqualFold(a,b)」。 </p></blockquote> <p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/024/63c224119dee6813.jpg" class="lazy" alt="go語言怎麼比較字串" ></p> <p>本教學操作環境：windows7系統、GO 1.18版本、Dell G3電腦。 </p> <h2 id="strong-Go語言比較字串方式-strong"><strong>Go語言比較字串方式</strong></h2> <p>在go 語言中字串比較的方式有以下三種：</p> <ul class="ul-level-0"> <li> <code> ==</code> 直接比較，區分大小寫</li> <li> <code>strings.Compare(a,b)</code> 此函數傳回值為int, 0 表示兩數相等，1 表示a>b, -1 表示a<b><li> <code>strings.EqualFold(a,b)</code> 直接回傳是否相等，不區分大小寫。 </li></b> </li> </ul> <p>範例如下：<span style="background-color: rgb(248, 248, 248);">// 1-使用等號比較－區分大消息</span></p> <div class="developer-code-block">#<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>func Equal(s1, s2 string) bool { return s1 == s2 } // 2-使用 compare 比较——区分大小写 func Compare(s1, s2 string) bool { return strings.Compare(s1, s2) == 0 // } //3-EqualFold 比较——不区分大小写. case-fold 即大小写同一处理 func EqualFold(s1, s2 string) bool { return strings.EqualFold(s1, s2) } // 使用等号比较——忽略大小写 func Equal2(s1, s2 string) bool { return strings.ToLower(s1) == strings.ToLower(s2) } // 使用 compare 比较——不区分大小写 func Compare2(s1, s2 string) bool { return strings.Compare(strings.ToLower(s1), strings.ToLower(s2)) == 0 } func StringCompareTest() { fmt.Println("== 区分大小写", Equal("go", "Go")) //false fmt.Println("== 忽略大小写",Equal2("go", "Go")) //true fmt.Println("compare 区分大小写",Compare("go", "Go")) //false fmt.Println("compare 忽略大小写",Compare2("go", "Go")) //true fmt.Println("EqualFold 忽略大小写",EqualFold("go", "Go")) // true }</pre><div class="contentsignin">登入後複製</div></div></div><h2 id="strong-效能比較-strong"><strong>效能比較</strong></h2><p>下面的程式碼使用Benchmark 做簡單的效能比較，測試專案的目錄結構為：</p><p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/image/916/800/564/167367265364778go語言怎麼比較字串" class="lazy" title="167367265364778go語言怎麼比較字串" alt="go語言怎麼比較字串"/></p><p>詳細程式碼：</p><div class="developer-code-block"> <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>package test import ( "../str" "testing" ) func BenchmarkStrEqual(b *testing.B) { for i := 0; i < b.N; i++ { str.Equal("go", "Go") } } func BenchmarkStrEqual2(b *testing.B) { for i := 0; i < b.N; i++ { str.Equal2("go", "Go") } } func BenchmarkStrCompare(b *testing.B) { for i := 0; i < b.N; i++ { str.Compare("go", "Go") } } func BenchmarkStrCompare2(b *testing.B) { for i := 0; i < b.N; i++ { str.Compare2("go", "Go") } } func BenchmarkStrEqualFold(b *testing.B) { for i := 0; i < b.N; i++ { str.EqualFold("go", "Go") } }</pre><div class="contentsignin">登入後複製</div></div></div><p>測試結果如下：</p><p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/image/725/103/124/1673672666716944.png" class="lazy" title="1673672666716944.png" alt="go語言怎麼比較字串"/></p><p>透過上圖可以看出，效率最高的還是==</p><h2 id="strong-原始碼簡單分析-strong"><strong>原始碼簡單分析</strong></h2><h4 id="strong-strings-Compare-strong"><strong>1、strings.Compare</strong></h4><div class="developer-code-block"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>package strings // Compare returns an integer comparing two strings lexicographically. // The result will be 0 if a==b, -1 if a < b, and +1 if a > b. // // Compare is included only for symmetry with package bytes. // It is usually clearer and always faster to use the built-in // string comparison operators ==, <, >, and so on. func Compare(a, b string) int { // NOTE(rsc): This function does NOT call the runtime cmpstring function, // because we do not want to provide any performance justification for // using strings.Compare. Basically no one should use strings.Compare. // As the comment above says, it is here only for symmetry with package bytes. // If performance is important, the compiler should be changed to recognize // the pattern so that all code doing three-way comparisons, not just code // using strings.Compare, can benefit. if a == b { return 0 } if a < b { return -1 } return +1 }</pre><div class="contentsignin">登入後複製</div></div></div><p>如上所示，我們發現，Compare 內部也是呼叫了<code>= =</code> , 而且函數的註解中也說了，這個函數only for symmetry with package bytes。而且推薦我們直接使用 <code>==</code> 和 <code>></code>、<code><</code>。 </p><h4 id="strong-strings-EqualFold-strong"><strong>2、strings.EqualFold</strong></h4><div class="developer-code-block"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class='brush:php;toolbar:false;'>// EqualFold reports whether s and t, interpreted as UTF-8 strings, // are equal under Unicode case-folding, which is a more general // form of case-insensitivity. func EqualFold(s, t string) bool { for s != "" && t != "" { // Extract first rune from each string. var sr, tr rune if s[0] < utf8.RuneSelf { sr, s = rune(s[0]), s[1:] } else { r, size := utf8.DecodeRuneInString(s) sr, s = r, s[size:] } if t[0] < utf8.RuneSelf { tr, t = rune(t[0]), t[1:] } else { r, size := utf8.DecodeRuneInString(t) tr, t = r, t[size:] } // If they match, keep going; if not, return false. // Easy case. if tr == sr { continue } // Make sr < tr to simplify what follows. if tr < sr { tr, sr = sr, tr } // Fast check for ASCII. if tr < utf8.RuneSelf { // ASCII only, sr/tr must be upper/lower case if &#39;A&#39; <= sr && sr <= &#39;Z&#39; && tr == sr+&#39;a&#39;-&#39;A&#39; { continue } return false } // General case. SimpleFold(x) returns the next equivalent rune > x // or wraps around to smaller values. r := unicode.SimpleFold(sr) for r != sr && r < tr { r = unicode.SimpleFold(r) } if r == tr { continue } return false } // One string is empty. Are both? return s == t }</pre><div class="contentsignin">登入後複製</div></div></div> <p>這個函數中做了一系列操作，將兩個字串轉換成<code>utf -8</code> 字串進行比較，並且在比較時忽略大小寫。 </p> <h2 id="strong-總結-strong"><strong>總結</strong></h2> <p>透過上面的簡單總結與分析，我們發現，字串比較還是直接用== 、>、 </p> <p>【相關推薦：<a href="http://www.php.cn/course/list/44.html" target="_blank">Go影片教學</a>、<a href="https://www.php.cn/course.html" target="_blank" textvalue="编程教学">程式設計教學</a>】</p>

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