.net String.IndexOf(char)真的比手动搜索慢吗?
在做一个简单的性能度量时,我惊讶地发现调用.net String.IndexOf(char)真的比手动搜索慢吗?,.net,performance,string,.net,Performance,String,在做一个简单的性能度量时,我惊讶地发现调用String.IndexOf(char)实际上比手动执行要慢!这是真的吗?!以下是我的测试代码: const string str = @"91023m lkajsdfl;jkasdf;piou-09324\\adf \asdf\45\ 65u\ 86\ 8\\\;"; static int testIndexOf() { return str.IndexOf('\\'); } static int testManualIndexOf() { s
String.IndexOf(char)
实际上比手动执行要慢!这是真的吗?!以下是我的测试代码:
const string str = @"91023m lkajsdfl;jkasdf;piou-09324\\adf \asdf\45\ 65u\ 86\ 8\\\;";
static int testIndexOf() { return str.IndexOf('\\'); }
static int testManualIndexOf() {
string s = str;
for (int i = 0; i < s.Length; ++i)
if (s[i] == '\\') return i;
return -1;
}
我至少运行了20次这些测试,每次都得到几乎相同的结果。我的机器是XP SP3,VS 2008 SP1,P4 3.0 GHz,没有超线程和1 GB RAM。我觉得结果真的很奇怪。如您所见,String.IndexOf
比我的PublicIndexOf
慢33%。更奇怪的是,我编写了与内部
相同的方法,它比公共
方法慢了大约8%!我不明白发生了什么,我希望你能帮助我理解
下面是测试代码。(很抱歉重复了代码,但我发现使用委托显示了不同的计时,而public
和internal
方法占用了相同的时间。)
公共静态类MyString{
public static int PublicIndexOf(字符串str,字符值){
对于(int i=0;i=str.Length)
抛出新ArgumentOutOfRangeException(“startIndex”);
对于(;startIndex=str.Length)
抛出新ArgumentOutOfRangeException(“startIndex”);
对于(;startIndex
下载.net framework的代码,看看str.IndexOf的真正功能,难道不可能吗 这个特定搜索的时间真的很关键,还是你在做致命的“无缘无故优化”?你试过用短的和长的弦吗?使用不同的搜索字符串?内置功能可能会针对其他情况进行优化,在这些情况下,搜索速度可能会较慢,而您的特定情况最终会较慢。我不会谴责IndexOf API“总是比较慢”,除非我对更多的情况做了更多的测试。即使它“手动”做得更快,也不明智。在你的.net版本中,你的CLR设置可能会更快。大概至少对于那个特定的字符串。但是你可以非常肯定的是,随着时间的推移,内置软件会有更好的改进机会。用你的语言。IndexOf也更加清晰。也许这25%是调用函数的成本
您的方法(testManualIndexOf)不调用任何函数。首先,您会有额外的函数调用开销。您是否尝试过将手动搜索包装在一个方法中并从测试中调用它——这确实是最好的比较,因为您不太可能每次都希望在字符串中搜索字符时编写该循环。您的测试并不公平,因为您没有实现相同的功能:
IndexOf
方法中传递参数时相比,需要执行的操作代码更少IndexOf
测试实际上进行了两次方法调用,而不是一次。很可能外部方法调用将内联到未在调试器下运行的发布版本中,但您的测试没有指明运行它的条件(如果是这种情况,那么您可以忽略这一点)但从本质上讲,考虑到您的方法所做的工作较少,我并不奇怪它运行得更快。正如前面所说的,我认为函数调用可能会导致一些问题
- String. IndexOf : 00:00:07.6490042
- MyString.PublicIndexOf : 00:00:05.6676471
- MyString.InternIndexOf : 00:00:06.1191796
- MyString.PublicIndexOf2: 00:00:09.1363687
- MyString.InternIndexOf2: 00:00:09.1182569
public static class MyString {
public static int PublicIndexOf(string str, char value) {
for (int i = 0; i < str.Length; ++i)
if (str[i] == value) return i;
return -1;
}
internal static int InternIndexOf(string str, char value) {
for (int i = 0; i < str.Length; ++i)
if (str[i] == value) return i;
return -1;
}
public static int PublicIndexOf2(string str, char value, int startIndex) {
if (startIndex < 0 || startIndex >= str.Length)
throw new ArgumentOutOfRangeException("startIndex");
for (; startIndex < str.Length; ++startIndex)
if (str[startIndex] == value) return startIndex;
return -1;
}
internal static int InternIndexOf2(string str, char value, int startIndex) {
if (startIndex < 0 || startIndex >= str.Length)
throw new ArgumentOutOfRangeException("startIndex");
for (; startIndex < str.Length; ++startIndex)
if (str[startIndex] == value) return startIndex;
return -1;
}
}
class Program {
static void Main(string[] args) {
int iterations = 100 * 1000 * 1000; // 100 millions
char separator = '\\';
string str = @"91023m lkajsdfl;jkasdf;piou-09324\\adf \asdf\45\ 65u\ 86\ 8\\\;";
Stopwatch watch = new Stopwatch();
// test String.IndexOf
int sum = 0;
watch.Start();
for (int i = 0; i < iterations; ++i)
sum += str.IndexOf(separator);
watch.Stop();
Console.WriteLine(" String. IndexOf : ({0}, {1})", watch.Elapsed, sum);
// test MyString.PublicIndexOf
sum = 0;
watch.Reset(); watch.Start();
for (int i = 0; i < iterations; ++i)
sum += MyString.PublicIndexOf(str, separator);
watch.Stop();
Console.WriteLine("MyString.PublicIndexOf : ({0}, {1})", watch.Elapsed, sum);
// test MyString.InternIndexOf
sum = 0;
watch.Reset(); watch.Start();
for (int i = 0; i < iterations; ++i)
sum += MyString.InternIndexOf(str, separator);
watch.Stop();
Console.WriteLine("MyString.InternIndexOf : ({0}, {1})", watch.Elapsed, sum);
// test MyString.PublicIndexOf2
sum = 0;
watch.Reset(); watch.Start();
for (int i = 0; i < iterations; ++i)
sum += MyString.PublicIndexOf2(str, separator,0);
watch.Stop();
Console.WriteLine("MyString.PublicIndexOf2: ({0}, {1})", watch.Elapsed, sum);
// test MyString.InternIndexOf2
sum = 0;
watch.Reset(); watch.Start();
for (int i = 0; i < iterations; ++i)
sum += MyString.InternIndexOf2(str, separator,0);
watch.Stop();
Console.WriteLine("MyString.InternIndexOf2: ({0}, {1})", watch.Elapsed, sum);
}
}
static void Main(string[] args)
{
{
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 25000000; i++)
testIndexOf();
sw.Stop();
Console.WriteLine(sw.Elapsed); //2.27 s
}
{
Stopwatch sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 25000000; i++)
testManualIndexOf();
sw.Stop();
Console.WriteLine(sw.Elapsed); //9.81 s
}
Console.ReadLine();
}
String. IndexOf : (00:00:06.3134669, -994967296)
MyString.PublicIndexOf : (00:00:07.0769368, -994967296)
MyString.InternIndexOf : (00:00:08.3463652, -994967296)
MyString.PublicIndexOf2: (00:00:12.0049268, -994967296)
MyString.InternIndexOf2: (00:00:12.4344756, -994967296)
static void Main()
{
const int LOOP = 25000000;
int chk1 = 0, chk2 = 0;
Stopwatch watch1 = Stopwatch.StartNew();
for (int i = 0; i < LOOP; i++)
{
chk1 += testIndexOf();
}
watch1.Stop();
Stopwatch watch2 = Stopwatch.StartNew();
for (int i = 0; i < LOOP; i++)
{
chk2 += testManualIndexOf();
}
watch2.Stop();
Console.WriteLine("{0}ms, ({1})", watch1.ElapsedMilliseconds, chk1);
Console.WriteLine("{0}ms, ({1})", watch2.ElapsedMilliseconds, chk2);
}
public static void Main(string[] args) {
int nTrials = 10000000;
Random rg = new Random(1);
Stopwatch sw = new Stopwatch();
for (int i = 0; i < nTrials; i++) {
int len = 1 + rg.Next(250);
char[] randomChar = new char[len];
for(int j = 0; j < len; j++) {
randomChar[j] = GetRandomLetterOrDigit(rg);
}
string s = new string(randomChar);
char findChar = GetRandomLetterOrDigit(rg);
sw.Start();
int index = s.IndexOf(findChar);
//int index = testManualIndexOf(s, findChar);
sw.Stop();
}
Console.WriteLine(sw.ElapsedMilliseconds);
}
private static char GetRandomLetterOrDigit(Random rg) {
char c;
int rc = rg.Next(62);
if (rc < 26) {
c = (char)('A' + rc);
}
else if (rc < 52) {
c = (char)('a' + rc - 26);
}
else {
c = (char)('0' + rc - 52);
}
return c;
}
private static int testManualIndexOf(string s, char c) {
if (s == null) {
throw new ArgumentNullException("s");
}
for (int i = 0; i < s.Length; ++i) {
if (s[i] == c) return i;
}
return -1;
}