You can use a non-capturing lambda function with C-style APIs that expect a function pointer. As long as the signatures of the callback and the lambda match, the lambda will be cast to a function pointer (or you could define a “positive lambda”, one with a 

+
in front of it; this causes automatic conversion to a function pointer). This works because the compiler converts non-capturing lambdas to actual functions and stores them inside the compiled binary. Effectively a pointer to locally defined lambda is valid for the life of the program.

In the program below I define a callback with the following signature: 

typedef void(*FuncPtr)(int arg)
and two C-style functions that use it: 
void set_callback(FuncPtr fp)
and 
void fire_callback(int arg)
. I then call 
set_callback
with a positive lambda. The program works 🙂

c_api_lambda.cpp:

#include 

using namespace std;

typedef void(*FuncPtr)(int arg);
FuncPtr callback;

void set_callback(FuncPtr fp) { callback = fp; }
void fire_callback(int arg) { callback(arg); }

int main()
{
	set_callback(+[](int arg) { cout << arg << endl; });
	fire_callback(42);
}

42

Program output.

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