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PerformanceCounter Constructor (String, String, String, Boolean)

Initializes a new, read-only or read/write instance of the PerformanceCounter class and associates it with the specified system or custom performance counter and category instance on the local computer.

Namespace:  System.Diagnostics
Assembly:  System (in System.dll)

public PerformanceCounter(
	string categoryName,
	string counterName,
	string instanceName,
	bool readOnly


Type: System.String

The name of the performance counter category (performance object) with which this performance counter is associated.

Type: System.String

The name of the performance counter.

Type: System.String

The name of the performance counter category instance, or an empty string (""), if the category contains a single instance.

Type: System.Boolean

true to access a counter in read-only mode; false to access a counter in read/write mode.


categoryName is an empty string ("").


counterName is an empty string ("").


The read/write permission setting requested is invalid for this counter.


The category specified does not exist (if readOnly is true).


The category specified is not a .NET Framework custom category (if readOnly is false).


The category specified is marked as multi-instance and requires the performance counter to be created with an instance name.


instanceName is longer than 127 characters.


categoryName and counterName have been localized into different languages.


categoryName or counterName is null.


An error occurred when accessing a system API.


The platform is Windows 98 or Windows Millennium Edition (Me), which does not support performance counters.


Code that is executing without administrative privileges attempted to read a performance counter.

The parameter strings are not case-sensitive.

Use this overload to access a performance counter in either read-only or read/write mode.

This overload of the constructor sets the CategoryName, CounterName, and InstanceName properties to the values you pass in, it and sets the MachineName property to the local computer, ".".

This constructor initializes the performance counter and associates the instance with an existing counter (either a system or a custom counter) on the local computer. The values that you pass in for the CategoryName, CounterName, and InstanceName properties must point to an existing performance counter on the local computer. If the performance counter instance that you point to is not valid, calling the constructor throws an exception.


You can use this overload to connect to a system counter, but you cannot write to a system counter. Therefore, setting readOnly to false when connecting to a system counter causes the constructor to throw an exception.

To create a performance category instance, specify an instanceName on the PerformanceCounter constructor. If the category instance specified by instanceName already exists the new object will reference the existing category instance.


To read performance counters in Windows Vista, Windows XP Professional x64 Edition, or Windows Server 2003, you must either be a member of the Performance Monitor Users group or have administrative privileges.

To avoid having to elevate your privileges to access performance counters in Windows Vista, add yourself to the Performance Monitor Users group.

In Windows Vista, User Account Control (UAC) determines the privileges of a user. If you are a member of the Built-in Administrators group, you are assigned two run-time access tokens: a standard user access token and an administrator access token. By default, you are in the standard user role. To execute the code that accesses performance counters, you must first elevate your privileges from standard user to administrator. You can do this when you start an application by right-clicking the application icon and indicating that you want to run as an administrator.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0