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Debug.Assert Method (Boolean, String, String, Object[])

Checks for a condition; if the condition is false, outputs two messages (simple and formatted) and displays a message box that shows the call stack.

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

public static void Assert(
	bool condition,
	string message,
	string detailMessageFormat,
	params Object[] args


Type: System.Boolean
The conditional expression to evaluate. If the condition is true, the specified messages are not sent and the message box is not displayed.
Type: System.String
The message to send to the Listeners collection.
Type: System.String
The composite format string (see Remarks) to send to the Listeners collection. This message contains text intermixed with zero or more format items, which correspond to objects in the args array.
Type: System.Object[]
An object array that contains zero or more objects to format.

This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its text representation and embed that representation in a string. The resulting string is sent to the Listeners collection.

By default, the Debug.Assert method works only in debug builds. Use the Trace.Assert method if you want to do assertions in release builds. For more information, see Assertions in Managed Code.

Typically, the Assert(Boolean, String, String, Object[]) method is used to identify logic errors during program development. Assert evaluates the condition. If the result is false, The String.Format(String, Object[]) method is called and the detailMessageFormat string and args array are passed in as parameters. Assert(Boolean, String, String, Object[]) then sends the specified text message and the formatted text message to the Listeners collection. You can customize this behavior by adding a TraceListener to, or removing one from, the Listeners collection.

When the application runs in user-interface mode, it displays a message box that shows the call stack with file and line numbers. The message box contains three buttons: Abort, Retry, and Ignore. Clicking the Abort button terminates the application. Clicking Retry sends you to the code in the debugger if your application is running in a debugger, or offers to open a debugger if it is not. Clicking Ignore continues with the next instruction in the code.


The display of the message box is dependent on the presence of the DefaultTraceListener. If the DefaultTraceListener is not in the Listeners collection, the message box is not displayed. The DefaultTraceListener can be removed by the <clear> Element for <listeners> for <trace>, the <remove> Element for <listeners> for <trace>, or by calling the Clear method on the Listeners property (System.Diagnostics.Trace.Listeners.Clear()).

You can change the behavior of the DefaultTraceListener in the configuration file that corresponds to the name of your application. In this file, you can enable and disable the assert message box or set the DefaultTraceListener.LogFileName property. The configuration file should be formatted as follows:

    <assert assertuienabled="true" logfilename="c:\\myFile.log" />

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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