How to: Accept Variable Arguments
This example shows how functions with a variable number of arguments can be implemented in C++ using the ... syntax.
The parameter that uses ... must be the last parameter in the parameter list.
Example
// mcppv2_paramarray.cpp
// compile with: /clr
using namespace System;
double average( ... array<Int32>^ arr ) {
int i = arr->GetLength(0);
double answer = 0.0;
for (int j = 0 ; j < i ; j++)
answer += arr[j];
return answer / i;
}
int main() {
Console::WriteLine("{0}", average( 1, 2, 3, 6 ));
}
Output
3
Legacy Code Example
The following example shows how to call a C++ function that takes a variable number of arguments from C#.
// mcppv2_paramarray2.cpp
// compile with: /clr:safe /LD
using namespace System;
public ref class C {
public:
void f( ... array<String^>^ a ) {}
};
The function f can be called from C# or Visual Basic, for example, as though it were a function that can take a variable number of arguments.
In C#, an argument passed to a ParamArray parameter can be called with a variable number of arguments. The following code sample is in C#.
// mcppv2_paramarray3.cs
// compile with: /r:mcppv2_paramarray2.dll
// a C# program
public class X {
public static void Main() {
// Visual C# will generate a String array to match the
// ParamArray attribute
C myc = new C();
myc.f("hello", "there", "world");
}
}
A call to f in Visual C++ can pass an initialized array as well as a variable-length array:
// mcpp_paramarray4.cpp
// compile with: /clr
using namespace System;
public ref class C {
public:
void f( ... array<String^>^ a ) {}
};
int main() {
C ^ myc = gcnew C();
myc->f("hello", "world", "!!!");
}