Expressions in the Debugger - Visual Studio (Windows) (2023)

Applies to: visual studyVisual Studio for Macvisual study code

The Visual Studio debugger includes an expression evaluator when you're insidefast guarddialog box,I'm watchingwindows ordirectwindow. The expression evaluator also worksbreaking pointwindows and many other places in the debugger.

The following sections describe expression evaluation restrictions for languages ​​supported by Visual Studio.

F# expressions are not supported

The F# expression is not recognized. If you are debugging F# code, you must convert the expression to C# syntax before entering the expression into a debug window or dialog. When translating expressions from F# to C#, it is important to remember that C# uses==operator to check for equality, while F# uses a unique=.

C++ expression

For information about using contextual operators with expressions in C++, seeEnvironment Operators (C++).

Expressions are not supported in C++

Constructors, destructors and conversions

You cannot explicitly or implicitly call an object's constructor or destructor. For example, the following expression explicitly calls the constructor and results in an error message:

my_date (2, 3, 1985)

The conversion function cannot be called if the target of the conversion is a class. This conversion includes the construction of the item. For example ifminimum scoreis an examplegrade C, which defines the conversion function operatoralmost point, the following expression results in an error:

(fixed point) my rating

You cannot call new or delete operators. For example, the following expressions are not supported:

date (2.3.1985)

preprocessor macros

The debugger does not support preprocessor macros. For example, if a constantvaluedeclared as:#define value 3, you cannot usevalueindeI'm watchingwindow. To avoid this limitation, you should replace#definitionUse numbers and functions whenever possible.

Using namespace declarations

you cannot useuse namespaceannouncement. To access a type name or variable outside the current namespace, the fully qualified name must be used.

anonymous namespace

Anonymous namespaces are not supported. Unable to add if you have the following codetry itfor the protective window:

namespace mars { namespace { int test = 0; }}int main(){ // Adding a clock to a test has no effect. March::test++; return 0; }

Use debug properties to maintain state

Debug properties give you a way to call certain C/C++ functions in expressions without changing the state of your application.

Debug properties:

• Guaranteed Safety: Running the debugger will not inherently destroy the debugging process.

• allowed under all conditions, even when side effects and functional evaluation are not allowed.

• It works in scenarios where normal function calls are not possible, such as debugging minidumps.

  Debugging properties can also make evaluating expressions more convenient. E.g,strncmp (str, "asd")Write in breakpoint mode fromstr[0] == 'a' && str[1] == 's' && str[2] == 'd')

C++/CLI - unsupported expression

• Broadcasts that include pointers or custom broadcasts are not supported.

• Comparing and assigning objects is not supported.

• Overloaded operators and overloaded functions are not supported.

• Encapsulation and decoding are not supported.

• SizeThe operator is not supported.

C# - Unsupported expression

dynamic object

You can use statically typed dynamic variables in debug expressions. when the object implementsIDynamicMetaObjectProvider dynamic meta object providerAfter evaluation in the watch window, a dynamic view node is added. Dynamic view nodes display object members but do not allow editing of member values.

The following features on dynamic objects are not supported:

• compound operator+=,-=,%=,/=, and*=

• Many versions, including numerical models and parameter types

• Method calls with more than two parameters

• Property getters with more than two parameters

• property setter with parameters

• is assigned to the indexer

• boolean operator&&and||

anonymous method

Creating new anonymous methods is not supported.

Visual Basic - Unsupported expression

dynamic object

You can use statically typed dynamic variables in debug expressions. when the object implementsIDynamicMetaObjectProvider dynamic meta object providerAfter evaluation in the watch window, a dynamic view node is added. Dynamic view nodes display object members but do not allow editing of member values.

The following features on dynamic objects are not supported:

• compound operator+=,-=,%=,/=, and*=

• Many versions, including numerical models and parameter types

• Method calls with more than two parameters

• Property getters with more than two parameters

• property setter with parameters

• is assigned to the indexer

• boolean operator&&and||

local constant

Local constants are not supported.

input alias

Entering aliases is not supported.

variable declaration

You cannot declare explicit new variables in the debugger window. However, you can assign new implicit variables insidedirectwindow. These implicit variables are covered only by the debugger session and cannot be accessed outside the debugger. For example stateØ = 5implicitly creates a new variableOhand assign the value 5 to it. Such implicit variables are of typePurposeUnless the debugger can infer the type.

unsupported keyword

• address

• end

• error

• Exit

• I am going

• When something goes wrong

• restore

• RETURN

• Election/Case

• I am waiting

• sync lock

• Shot

• try/catch/finally

• and

• Names or module level keywords likefinally belowthemeasurement unit.

See also

• Format specifications in C++
• Environment Operators (C++)
• Format Specifiers in C#
• dummy variable