Calling a C callback function from C++ via a lambda -

i have code in plain c static library:

extern "c" {     typedef void (__cdecl* visitchildren)(option*);     void __cdecl dovisitchildren(children* list, visitchildren visitor); } 

and i'm trying use c++ code (unit tests) using lambda.

... dovisitchildren(children, [&] (option* option) { ... }); 

i'm getting compiler error c2664 ... cannot convert parameter 2 'unittests::unittest1::testbuild::<lambda_b286d160b9bab3e09ab93cd59fc49f0b>' 'visitchildren'

if remove capture '&' compiles , works, need capture bits , bobs.

is possible?

a closure created lambda expression can implicitly converted function pointer, if not capture variables. also, converted pointer extern "c++" function, not extern "c" function, , technically incompatible types.

so no, can't this.

a hacky workaround store actual closure in global variable , pass callback invokes it. work if program single-threaded , dovisitchildren call not store callback later use.

std::function<void(option*)> callback; extern "c" void __cdecl invoke_callback(option* o) { callback(o); }  // ...  callback = [&] (option* option) { /* ... */ }; dovisitchildren(children, invoke_callback);