如何计算子串出现的次数？
如何计算子串出现的次数？
提问于 2013-03-23 02:31:57
假设我有一个这样的字符串：
MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";然后我想知道子串"OU=“在这个字符串中出现的次数。对于单个字符，可能会有如下内容：
int count = MyString.Split("OU=").Length - 1;但Split只适用于char，不适用于string。
另外，如何找到n个匹配项的位置？例如，字符串中第二个"OU="的位置？
如何解决这个问题？
回答 8
Stack Overflow用户
回答已采纳
发布于 2013-03-23 02:35:27
Regex.Matches(input, "OU=").CountStack Overflow用户
发布于 2013-03-23 02:48:20
您可以使用IndexOf查找所有匹配项及其位置
string MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
string stringToFind = "OU=";
List<int> positions = new List<int>();
int pos = 0;
while ((pos < MyString.Length) && (pos = MyString.IndexOf(stringToFind, pos)) != -1)
{
positions.Add(pos);
pos += stringToFind.Length();
}
Console.WriteLine("{0} occurrences", positions.Count);
foreach (var p in positions)
{
Console.WriteLine(p);
}您可以从正则表达式中获得相同的结果：
var matches = Regex.Matches(MyString, "OU=");
Console.WriteLine("{0} occurrences", matches.Count);
foreach (var m in matches)
{
Console.WriteLine(m.Index);
}主要区别是：
- 正则表达式代码较短
- 正则表达式代码分配一个集合和多个字符串。
- 可以编写IndexOf代码以立即输出位置，而不会创建独立的正则表达式代码可能会更快，但如果多次使用，字符串分配的组合开销可能会导致垃圾收集器上的负载更高。
如果我以内联方式编写这段代码，作为不经常使用的代码，我可能会使用正则表达式解决方案。如果我把它放到一个库中，作为一个经常使用的东西，我可能会选择IndexOf解决方案。
Stack Overflow用户
发布于 2013-03-23 02:50:42
(Clippy-mode:ON)
您看起来像是在解析一个LDAP查询！
是否要对其进行解析：
是否手动执行
- ？通过Win32调用转到"SplittingAndParsing"
- Automagically？转到“通过PInvoke使用Win32”
(Clippy-mode:OFF)
"SplittingAndParsing":
var MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
var chunksAsKvps = MyString
.Split(',')
.Select(chunk =>
{
var bits = chunk.Split('=');
return new KeyValuePair<string,string>(bits[0], bits[1]);
});
var allOUs = chunksAsKvps
.Where(kvp => kvp.Key.Equals("OU", StringComparison.OrdinalIgnoreCase));“通过PInvoke使用Win32”：
用法：
var parsedDn = Win32LDAP.ParseDN(str);
var allOUs2 = parsedDn
.Where(dn => dn.Key.Equals("OU", StringComparison.OrdinalIgnoreCase));实用程序代码：
// I don't remember where I got this from, honestly...I *think* it came
// from another SO user long ago, but those details I've lost to history...
public class Win32LDAP
{
#region Constants
public const int ERROR_SUCCESS = 0;
public const int ERROR_BUFFER_OVERFLOW = 111;
#endregion Constants
#region DN Parsing
[DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
protected static extern int DsGetRdnW(
ref IntPtr ppDN,
ref int pcDN,
out IntPtr ppKey,
out int pcKey,
out IntPtr ppVal,
out int pcVal
);
public static KeyValuePair<string, string> GetName(string distinguishedName)
{
IntPtr pDistinguishedName = Marshal.StringToHGlobalUni(distinguishedName);
try
{
IntPtr pDN = pDistinguishedName, pKey, pVal;
int cDN = distinguishedName.Length, cKey, cVal;
int lastError = DsGetRdnW(ref pDN, ref cDN, out pKey, out cKey, out pVal, out cVal);
if(lastError == ERROR_SUCCESS)
{
string key, value;
if(cKey < 1)
{
key = string.Empty;
}
else
{
key = Marshal.PtrToStringUni(pKey, cKey);
}
if(cVal < 1)
{
value = string.Empty;
}
else
{
value = Marshal.PtrToStringUni(pVal, cVal);
}
return new KeyValuePair<string, string>(key, value);
}
else
{
throw new Win32Exception(lastError);
}
}
finally
{
Marshal.FreeHGlobal(pDistinguishedName);
}
}
public static IEnumerable<KeyValuePair<string, string>> ParseDN(string distinguishedName)
{
List<KeyValuePair<string, string>> components = new List<KeyValuePair<string, string>>();
IntPtr pDistinguishedName = Marshal.StringToHGlobalUni(distinguishedName);
try
{
IntPtr pDN = pDistinguishedName, pKey, pVal;
int cDN = distinguishedName.Length, cKey, cVal;
do
{
int lastError = DsGetRdnW(ref pDN, ref cDN, out pKey, out cKey, out pVal, out cVal);
if(lastError == ERROR_SUCCESS)
{
string key, value;
if(cKey < 0)
{
key = null;
}
else if(cKey == 0)
{
key = string.Empty;
}
else
{
key = Marshal.PtrToStringUni(pKey, cKey);
}
if(cVal < 0)
{
value = null;
}
else if(cVal == 0)
{
value = string.Empty;
}
else
{
value = Marshal.PtrToStringUni(pVal, cVal);
}
components.Add(new KeyValuePair<string, string>(key, value));
pDN = (IntPtr)(pDN.ToInt64() + UnicodeEncoding.CharSize); //skip over comma
cDN--;
}
else
{
throw new Win32Exception(lastError);
}
} while(cDN > 0);
return components;
}
finally
{
Marshal.FreeHGlobal(pDistinguishedName);
}
}
[DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
protected static extern int DsQuoteRdnValueW(
int cUnquotedRdnValueLength,
string psUnquotedRdnValue,
ref int pcQuotedRdnValueLength,
IntPtr psQuotedRdnValue
);
public static string QuoteRDN(string rdn)
{
if (rdn == null) return null;
int initialLength = rdn.Length;
int quotedLength = 0;
IntPtr pQuotedRDN = IntPtr.Zero;
int lastError = DsQuoteRdnValueW(initialLength, rdn, ref quotedLength, pQuotedRDN);
switch (lastError)
{
case ERROR_SUCCESS:
{
return string.Empty;
}
case ERROR_BUFFER_OVERFLOW:
{
break; //continue
}
default:
{
throw new Win32Exception(lastError);
}
}
pQuotedRDN = Marshal.AllocHGlobal(quotedLength * UnicodeEncoding.CharSize);
try
{
lastError = DsQuoteRdnValueW(initialLength, rdn, ref quotedLength, pQuotedRDN);
switch(lastError)
{
case ERROR_SUCCESS:
{
return Marshal.PtrToStringUni(pQuotedRDN, quotedLength);
}
default:
{
throw new Win32Exception(lastError);
}
}
}
finally
{
if(pQuotedRDN != IntPtr.Zero)
{
Marshal.FreeHGlobal(pQuotedRDN);
}
}
}
[DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
protected static extern int DsUnquoteRdnValueW(
int cQuotedRdnValueLength,
string psQuotedRdnValue,
ref int pcUnquotedRdnValueLength,
IntPtr psUnquotedRdnValue
);
public static string UnquoteRDN(string rdn)
{
if (rdn == null) return null;
int initialLength = rdn.Length;
int unquotedLength = 0;
IntPtr pUnquotedRDN = IntPtr.Zero;
int lastError = DsUnquoteRdnValueW(initialLength, rdn, ref unquotedLength, pUnquotedRDN);
switch (lastError)
{
case ERROR_SUCCESS:
{
return string.Empty;
}
case ERROR_BUFFER_OVERFLOW:
{
break; //continue
}
default:
{
throw new Win32Exception(lastError);
}
}
pUnquotedRDN = Marshal.AllocHGlobal(unquotedLength * UnicodeEncoding.CharSize);
try
{
lastError = DsUnquoteRdnValueW(initialLength, rdn, ref unquotedLength, pUnquotedRDN);
switch(lastError)
{
case ERROR_SUCCESS:
{
return Marshal.PtrToStringUni(pUnquotedRDN, unquotedLength);
}
default:
{
throw new Win32Exception(lastError);
}
}
}
finally
{
if(pUnquotedRDN != IntPtr.Zero)
{
Marshal.FreeHGlobal(pUnquotedRDN);
}
}
}
#endregion DN Parsing
}
public class DNComponent
{
public string Type { get; protected set; }
public string EscapedValue { get; protected set; }
public string UnescapedValue { get; protected set; }
public string WholeComponent { get; protected set; }
public DNComponent(string component, bool isEscaped)
{
string[] tokens = component.Split(new char[] { '=' }, 2);
setup(tokens[0], tokens[1], isEscaped);
}
public DNComponent(string key, string value, bool isEscaped)
{
setup(key, value, isEscaped);
}
private void setup(string key, string value, bool isEscaped)
{
Type = key;
if(isEscaped)
{
EscapedValue = value;
UnescapedValue = Win32LDAP.UnquoteRDN(value);
}
else
{
EscapedValue = Win32LDAP.QuoteRDN(value);
UnescapedValue = value;
}
WholeComponent = Type + "=" + EscapedValue;
}
public override bool Equals(object obj)
{
if (obj is DNComponent)
{
DNComponent dnObj = (DNComponent)obj;
return dnObj.WholeComponent.Equals(this.WholeComponent, StringComparison.CurrentCultureIgnoreCase);
}
return base.Equals(obj);
}
public override int GetHashCode()
{
return WholeComponent.GetHashCode();
}
}
public class DistinguishedName
{
public DNComponent[] Components
{
get
{
return components.ToArray();
}
}
private List<DNComponent> components;
private string cachedDN;
public DistinguishedName(string distinguishedName)
{
cachedDN = distinguishedName;
components = new List<DNComponent>();
foreach (KeyValuePair<string, string> kvp in Win32LDAP.ParseDN(distinguishedName))
{
components.Add(new DNComponent(kvp.Key, kvp.Value, true));
}
}
public DistinguishedName(IEnumerable<DNComponent> dnComponents)
{
components = new List<DNComponent>(dnComponents);
cachedDN = GetWholePath(",");
}
public bool Contains(DNComponent dnComponent)
{
return components.Contains(dnComponent);
}
public string GetDNSDomainName()
{
List<string> dcs = new List<string>();
foreach (DNComponent dnc in components)
{
if(dnc.Type.Equals("DC", StringComparison.CurrentCultureIgnoreCase))
{
dcs.Add(dnc.UnescapedValue);
}
}
return string.Join(".", dcs.ToArray());
}
public string GetDomainDN()
{
List<string> dcs = new List<string>();
foreach (DNComponent dnc in components)
{
if(dnc.Type.Equals("DC", StringComparison.CurrentCultureIgnoreCase))
{
dcs.Add(dnc.WholeComponent);
}
}
return string.Join(",", dcs.ToArray());
}
public string GetWholePath()
{
return GetWholePath(",");
}
public string GetWholePath(string separator)
{
List<string> parts = new List<string>();
foreach (DNComponent component in components)
{
parts.Add(component.WholeComponent);
}
return string.Join(separator, parts.ToArray());
}
public DistinguishedName GetParent()
{
if(components.Count == 1)
{
return null;
}
List<DNComponent> tempList = new List<DNComponent>(components);
tempList.RemoveAt(0);
return new DistinguishedName(tempList);
}
public override bool Equals(object obj)
{
if(obj is DistinguishedName)
{
DistinguishedName objDN = (DistinguishedName)obj;
if (this.Components.Length == objDN.Components.Length)
{
for (int i = 0; i < this.Components.Length; i++)
{
if (!this.Components[i].Equals(objDN.Components[i]))
{
return false;
}
}
return true;
}
return false;
}
return base.Equals(obj);
}
public override int GetHashCode()
{
return cachedDN.GetHashCode();
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/15577464
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