- Strings in C#: == vs .Equals<P>I've heard a few times that .Equals is better than == for comparing strings in C#. To test this, I wrote a little C# program that called == a hundred million times, and then compared it with .Equals.</P>
<P>Here's the code:</P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN><SPAN style="COLOR: blue">string</SPAN> a = "hello";<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN><SPAN style="COLOR: blue">string</SPAN> b = "hello";<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN><SPAN style="COLOR: blue">int</SPAN> count = 0;<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN>DateTime start = DateTime.Now;<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><o:p> </o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN><SPAN style="COLOR: blue">for</SPAN> (<SPAN style="COLOR: blue">int</SPAN> i=0; i<100000000; i++)<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN>{<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 4"> </SPAN><SPAN style="COLOR: blue">if</SPAN> (a.Equals(b))<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 5"> </SPAN>count++;<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 4"> </SPAN><SPAN style="COLOR: blue">else<o:p></o:p></SPAN></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 5"> </SPAN>count++;<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN>};<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><o:p> </o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN>TimeSpan ts = DateTime.Now - start;<o:p></o:p></SPAN></P>
<P class=MsoNormal style="MARGIN: 0in 0in 0pt; mso-layout-grid-align: none"><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Courier New'"><SPAN style="mso-tab-count: 3"> </SPAN>Console.WriteLine("{0}", ts.Milliseconds);<o:p></o:p></SPAN></P>
<P>The results were interesting.. I did the test four times, twice changing the strings so they were not equal (changing string “b” to “jello” from “hello”) and twice using == instead of .Equals.</P>
<P>Here's the results:</P>
<DIV align=center>
<TABLE align=center border=1>
<TBODY>
<TR>
<TH>
<P align=center> </P></TH>
<TH>a == b</TH>
<TH>a.Equals(b)</TH></TR>
<TR>
<TD><STRONG>Equal strings</STRONG></TD>
<TD>961ms</TD>
<TD>655ms</TD></TR>
<TR>
<TD><STRONG>Differing strings</STRONG></TD>
<TD>750ms</TD>
<TD>890ms</TD></TR></TBODY></TABLE></DIV>
<P>So “a == b” is much slower when the strings are identical, and somewhat faster when the strings are different. But either way, I could compare these strings a hundred million times in less than a second. Another way to look at it is == is about 90% as fast as .Equals, on average (assuming your strings are the same about half the time).</P>
<P>Personally I think the difference is negligible and I prefer the readability of ==, but for performance-critical code it would make sense to think about whether you expect the strings to match or not match most of the time and choose the right one accordingly.</P>
<P> </P>Thu, 01 Sep 2005 19:17:07 GMT