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Compiler Error C3642

'return_type/args' : cannot call a function with __clrcall calling convention from native code

A function that is marked with the __clrcall calling convention cannot be called from native (unmanaged) code.

return_type/args is either the name of the function or the type of the __clrcall function you are trying to call. A type is used when you're calling through a function-pointer.

To call a managed function from a native context, you can add a "wrapper" function that will call the __clrcall function. Or, you can use the CLR marshalling mechanism; see How to: Marshal Function Pointers Using PInvoke for more information.

The following sample generates C3642:

// C3642.cpp
// compile with: /clr
using namespace System;
struct S {
   void Test(String ^ s) {   // CLR type in signature, implicitly __clrcall
   void Test2(char * s) {
      Test(gcnew String(s));

#pragma unmanaged
int main() {
   S s;
   s.Test("abc");   // C3642
   s.Test2("abc");   // OK