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The safe_cast operation returns the specified expression as the specified type. If the operation isn't successful, it throws an InvalidCastException.
All Runtimes
(There are no remarks for this language feature that apply to all runtimes.)
Syntax
[default]:: safe_cast< type-id >( expression )
Windows Runtime
Use safe_cast to change the type of a specified expression. If you expect a variable or parameter to be convertible to a certain type, use safe_cast without a try-catch block to detect programming errors during development. For more information, see Casting (C++/CX).
Syntax
[default]:: safe_cast< type-id >( expression )
Parameters
type-id
The type to convert expression to. A handle to a reference or value type, a value type, or a tracking reference to a reference or value type.
expression
An expression that evaluates to a handle to a reference or value type, a value type, or a tracking reference to a reference or value type.
Remarks
safe_cast throws InvalidCastException if it can't convert expression to the type specified by type-id. To catch InvalidCastException, specify the /EH (Exception Handling Model) compiler option, and use a try/catch statement.
Requirements
Compiler option: /ZW
Examples
The following code example demonstrates how to use safe_cast with the Windows Runtime.
// safe_cast_ZW.cpp
// compile with: /ZW /EHsc
using namespace default;
using namespace Platform;
interface class I1 {};
interface class I2 {};
interface class I3 {};
ref class X : public I1, public I2 {};
int main(Array<String^>^ args) {
I1^ i1 = ref new X;
I2^ i2 = safe_cast<I2^>(i1); // OK, I1 and I2 have common type: X
// I2^ i3 = static_cast<I2^>(i1); C2440 use safe_cast instead
try {
I3^ i4 = safe_cast<I3^>(i1); // Fails because i1 is not derived from I3.
}
catch(InvalidCastException^ ic) {
wprintf(L"Caught expected exception: %s\n", ic->Message);
}
}
Caught expected exception: InvalidCastException
Common Language Runtime
safe_cast changes the type of an expression and generates verifiable MSIL code.
Syntax
[cli]:: safe_cast< type-id >( expression )
Parameters
type-id
A handle to a reference or value type, a value type, or a tracking reference to a reference or value type.
expression
An expression that evaluates to a handle to a reference or value type, a value type, or a tracking reference to a reference or value type.
Remarks
The expression safe_cast<type-id>(expression) converts the operand expression to an object of type type-id.
The compiler accepts a static_cast in most places that it accepts a safe_cast. However, safe_cast always produces verifiable MSIL, whereas a static_cast might produce unverifiable MSIL. For more information on verifiable code, see Pure and Verifiable Code (C++/CLI) and Peverify.exe (PEVerify Tool).
Like static_cast, safe_cast invokes user-defined conversions.
For more information about casts, see Casting Operators.
safe_cast doesn't apply a const_cast (cast away const).
safe_cast is in the cli namespace. For more information, see Platform, default, and cli Namespaces.
For more information on safe_cast, see:
Requirements
Compiler option: /clr
Examples
One example of where the compiler doesn't accept a static_cast but accepts a safe_cast is for casts between unrelated interface types. With safe_cast, the compiler doesn't issue a conversion error and performs a check at runtime to see if the cast is possible.
// safe_cast.cpp
// compile with: /clr
using namespace System;
interface class I1 {};
interface class I2 {};
interface class I3 {};
ref class X : public I1, public I2 {};
int main() {
I1^ i1 = gcnew X;
I2^ i2 = safe_cast<I2^>(i1); // OK, I1 and I2 have common type: X
// I2^ i3 = static_cast<I2^>(i1); C2440 use safe_cast instead
try {
I3^ i4 = safe_cast<I3^>(i1); // fail at runtime, no common type
}
catch(InvalidCastException^) {
Console::WriteLine("Caught expected exception");
}
}
Caught expected exception