Callbacks

Questions 1 to 5 of 6

1. 1. Match each callable type to what it can do.

   Choose the matching item for each row.

   int (*op)(int)Choose…A callable that can hold captured variablesA function pointer, which holds only an addressThe compiler writes a separate version for each callable typestd::function<int(int)>Choose…A callable that can hold captured variablesA function pointer, which holds only an addressThe compiler writes a separate version for each callable typetemplate <typename F> int apply(F op, int start)Choose…A callable that can hold captured variablesA function pointer, which holds only an addressThe compiler writes a separate version for each callable type
2. 2. Match each error message to its cause.

   Choose the matching item for each row.

   cannot convert 'main()::<lambda(int)>' to 'IntOp'Choose…The callback's parameter and return types do not match the alias`int *op(int);` declared a function, not a pointer variableAn empty std::function was called without checking it firstThe lambda captures a variable, and a function pointer has nowhere to store itinvalid conversion from 'double (*)(double)' to 'IntOp'Choose…The callback's parameter and return types do not match the alias`int *op(int);` declared a function, not a pointer variableAn empty std::function was called without checking it firstThe lambda captures a variable, and a function pointer has nowhere to store itundefined reference to 'op(int)'Choose…The callback's parameter and return types do not match the alias`int *op(int);` declared a function, not a pointer variableAn empty std::function was called without checking it firstThe lambda captures a variable, and a function pointer has nowhere to store itterminate called after throwing an instance of 'std::bad_function_call'Choose…The callback's parameter and return types do not match the alias`int *op(int);` declared a function, not a pointer variableAn empty std::function was called without checking it firstThe lambda captures a variable, and a function pointer has nowhere to store it
3. 3. Predict the output of this program. ``cpp #include <iostream> using IntOp = int (*)(int); int apply_twice(IntOp op, int start) { return op(op(start)); } int main() { std::cout << apply_twice([](int n) { return n * n + 1; }, 2) << '\n'; } ``

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4. 4. Predict the output of this program. ``cpp #include <functional> #include <iostream> #include <vector> int main() { std::vector<std::function<int()>> jobs; int base = 3; jobs.push_back([base] { return base * 10; }); base = 7; jobs.push_back([&base] { return base * 10; }); std::cout << jobs[0]() << ' ' << jobs[1]() << '\n'; } ``

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5. 5. Which statement about std::function is correct?

   It can hold a lambda that captures variables by reference, and it can be stored in a vectorIt cannot be empty, so calling it never throwsCalling an empty one crashes with a segmentation faultIt holds only a memory address, like a plain function pointer