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    <p>(EDIT: See bottom of post for benchmarks on different micro-optimizations of the method)</p> <p>Don't trim it - that might create a new string which you don't actually need. Instead, look through the string for any characters that <em>aren't</em> whitespace (for whatever definition you want). For example:</p> <pre><code>public static bool IsEmptyOrWhitespace(string text) { // Avoid creating iterator for trivial case if (text.Length == 0) { return true; } foreach (char c in text) { // Could use Char.IsWhiteSpace(c) instead if (c==' ' || c=='\t' || c=='\r' || c=='\n') { continue; } return false; } return true; } </code></pre> <p>You might also consider what you want the method to do if <code>text</code> is <code>null</code>.</p> <p>Possible further micro-optimizations to experiment with:</p> <ul> <li><p>Is <code>foreach</code> faster or slower than using a <code>for</code> loop like the one below? Note that with the <code>for</code> loop you can remove the "<code>if (text.Length==0)</code>" test at the start.</p> <pre><code>for (int i = 0; i &lt; text.Length; i++) { char c = text[i]; // ... </code></pre></li> <li><p>Same as above, but hoisting the <code>Length</code> call. Note that this <em>isn't</em> good for normal arrays, but <em>might</em> be useful for strings. I haven't tested it.</p> <pre><code>int length = text.Length; for (int i = 0; i &lt; length; i++) { char c = text[i]; </code></pre></li> <li><p>In the body of the loop, is there any difference (in speed) between what we've got and:</p> <pre><code>if (c != ' ' &amp;&amp; c != '\t' &amp;&amp; c != '\r' &amp;&amp; c != '\n') { return false; } </code></pre></li> <li><p>Would a switch/case be faster?</p> <pre><code>switch (c) { case ' ': case '\r': case '\n': case '\t': return false; } </code></pre></li> </ul> <p><strong>Update on Trim behaviour</strong></p> <p>I've just been looking into how <code>Trim</code> can be as efficient as this. It seems that <code>Trim</code> will only create a new string if it needs to. If it can return <code>this</code> or <code>""</code> it will:</p> <pre><code>using System; class Test { static void Main() { CheckTrim(string.Copy("")); CheckTrim(" "); CheckTrim(" x "); CheckTrim("xx"); } static void CheckTrim(string text) { string trimmed = text.Trim(); Console.WriteLine ("Text: '{0}'", text); Console.WriteLine ("Trimmed ref == text? {0}", object.ReferenceEquals(text, trimmed)); Console.WriteLine ("Trimmed ref == \"\"? {0}", object.ReferenceEquals("", trimmed)); Console.WriteLine(); } } </code></pre> <p>This means it's really important that any benchmarks in this question should use a mixture of data:</p> <ul> <li>Empty string</li> <li>Whitespace</li> <li>Whitespace surrounding text</li> <li>Text without whitespace</li> </ul> <p>Of course, the "real world" balance between these four is impossible to predict...</p> <p><strong>Benchmarks</strong> I've run some benchmarks of the original suggestions vs mine, and mine appears to win in everything I throw at it, which surprises me given the results in other answers. However, I've also benchmarked the difference between <code>foreach</code>, <code>for</code> using <code>text.Length</code>, <code>for</code> using <code>text.Length</code> once and then reversing the iteration order, and <code>for</code> with a hoisted length.</p> <p>Basically the <code>for</code> loop is very slightly faster, but hoisting the length check makes it slower than <code>foreach</code>. Reversing the <code>for</code> loop direction is very slightly slower than <code>foreach</code> too. I strongly suspect that the JIT is doing interesting things here, in terms of removing duplicate bounds checks etc.</p> <p>Code: (see <a href="http://msmvps.com/blogs/jon_skeet/archive/2009/01/26/benchmarking-made-easy.aspx" rel="noreferrer">my benchmarking blog entry</a> for the framework this is written against)</p> <pre><code>using System; using BenchmarkHelper; public class TrimStrings { static void Main() { Test(""); Test(" "); Test(" x "); Test("x"); Test(new string('x', 1000)); Test(" " + new string('x', 1000) + " "); Test(new string(' ', 1000)); } static void Test(string text) { bool expectedResult = text.Trim().Length == 0; string title = string.Format("Length={0}, result={1}", text.Length, expectedResult); var results = TestSuite.Create(title, text, expectedResult) /* .Add(x =&gt; x.Trim().Length == 0, "Trim().Length == 0") .Add(x =&gt; x.Trim() == "", "Trim() == \"\"") .Add(x =&gt; x.Trim().Equals(""), "Trim().Equals(\"\")") .Add(x =&gt; x.Trim() == string.Empty, "Trim() == string.Empty") .Add(x =&gt; x.Trim().Equals(string.Empty), "Trim().Equals(string.Empty)") */ .Add(OriginalIsEmptyOrWhitespace) .Add(IsEmptyOrWhitespaceForLoop) .Add(IsEmptyOrWhitespaceForLoopReversed) .Add(IsEmptyOrWhitespaceForLoopHoistedLength) .RunTests() .ScaleByBest(ScalingMode.VaryDuration); results.Display(ResultColumns.NameAndDuration | ResultColumns.Score, results.FindBest()); } public static bool OriginalIsEmptyOrWhitespace(string text) { if (text.Length == 0) { return true; } foreach (char c in text) { if (c==' ' || c=='\t' || c=='\r' || c=='\n') { continue; } return false; } return true; } public static bool IsEmptyOrWhitespaceForLoop(string text) { for (int i=0; i &lt; text.Length; i++) { char c = text[i]; if (c==' ' || c=='\t' || c=='\r' || c=='\n') { continue; } return false; } return true; } public static bool IsEmptyOrWhitespaceForLoopReversed(string text) { for (int i=text.Length-1; i &gt;= 0; i--) { char c = text[i]; if (c==' ' || c=='\t' || c=='\r' || c=='\n') { continue; } return false; } return true; } public static bool IsEmptyOrWhitespaceForLoopHoistedLength(string text) { int length = text.Length; for (int i=0; i &lt; length; i++) { char c = text[i]; if (c==' ' || c=='\t' || c=='\r' || c=='\n') { continue; } return false; } return true; } } </code></pre> <p>Results:</p> <pre><code>============ Length=0, result=True ============ OriginalIsEmptyOrWhitespace 30.012 1.00 IsEmptyOrWhitespaceForLoop 30.802 1.03 IsEmptyOrWhitespaceForLoopReversed 32.944 1.10 IsEmptyOrWhitespaceForLoopHoistedLength 35.113 1.17 ============ Length=1, result=True ============ OriginalIsEmptyOrWhitespace 31.150 1.04 IsEmptyOrWhitespaceForLoop 30.051 1.00 IsEmptyOrWhitespaceForLoopReversed 31.602 1.05 IsEmptyOrWhitespaceForLoopHoistedLength 33.383 1.11 ============ Length=3, result=False ============ OriginalIsEmptyOrWhitespace 30.221 1.00 IsEmptyOrWhitespaceForLoop 30.131 1.00 IsEmptyOrWhitespaceForLoopReversed 34.502 1.15 IsEmptyOrWhitespaceForLoopHoistedLength 35.690 1.18 ============ Length=1, result=False ============ OriginalIsEmptyOrWhitespace 31.626 1.05 IsEmptyOrWhitespaceForLoop 30.005 1.00 IsEmptyOrWhitespaceForLoopReversed 32.383 1.08 IsEmptyOrWhitespaceForLoopHoistedLength 33.666 1.12 ============ Length=1000, result=False ============ OriginalIsEmptyOrWhitespace 30.177 1.00 IsEmptyOrWhitespaceForLoop 33.207 1.10 IsEmptyOrWhitespaceForLoopReversed 30.867 1.02 IsEmptyOrWhitespaceForLoopHoistedLength 31.837 1.06 ============ Length=1002, result=False ============ OriginalIsEmptyOrWhitespace 30.217 1.01 IsEmptyOrWhitespaceForLoop 30.026 1.00 IsEmptyOrWhitespaceForLoopReversed 34.162 1.14 IsEmptyOrWhitespaceForLoopHoistedLength 34.860 1.16 ============ Length=1000, result=True ============ OriginalIsEmptyOrWhitespace 30.303 1.01 IsEmptyOrWhitespaceForLoop 30.018 1.00 IsEmptyOrWhitespaceForLoopReversed 35.475 1.18 IsEmptyOrWhitespaceForLoopHoistedLength 40.927 1.36 </code></pre>
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    1. POWhat's the most efficient way to determine whether an untrimmed string is empty in C#?
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    1. COWill the foreach(char c in text) actually do an inline search or will it create a new array of chars?
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    2. COIt will create an appropriate IEnumerator<char> associated with the string. It doesn't copy the string.
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    3. COI've just tested this method with a million iterations - it's slightly slower than using Trim(). I guess you might save a bit down the line, though, through avoiding GC.
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      1. USJoe Albahari
 

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