How to code std::lock_guard<std::mutex> l(m)?

Question

template<typename T>
class threadsafe_stack
{
// Sharing data between threads
private:
std::stack<T> data;
mutable std::mutex m;
public:
...

std::lock_guard<std::mutex> l(m);

I get the error in Sololearn: 'm' is no type.
What is here wrong coded, or is it a problem of the Sololearn C++ Compiler?

Answer 1

It seems to work:
https://code.sololearn.com/cJ1Q1BdCKOZg/?ref=app

Answer 2

Yes. 'm' is a private member of the class threadsafe_stack. The std::lock_guard<std::mutex> l(m); is a function call inside this class. Why is it not compilable without this error?

Answer 3

Thank you all. I found the fault. I missed a } bracket at the end of a function definition.