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Hi I am working on this project and in the header the file the following is defined
typedef std::function<unsigned int(const std::string&)> HashFunction;
How exactly do i use this with my HashFunction? When I try
HashFunction myHashFunction;
myHashFunction("mystring");
the program crashes.
801
In this tutorial, we will learn about the typedef function and typedef function pointer in C programming language. The typedef is a keyword in the C to provide some meaningful and easy-to-understand names to the already existing variables. It behaves similarly as we define the alias name for any command in a C program.
A typedef, or a function-type alias, helps to define pointers to executable code within memory. Simply put, a typedef can be used as a pointer that references a function. Given below are the steps to implement typedefs in a Dart program.
Instances of std::function can store, copy, and invoke any CopyConstructible Callable target -- functions (via pointers thereto), lambda expressions, bind expressions, or other function objects, as well as pointers to member functions and pointers to data members.
h> void upton(int n) { for (int i = 1; i <= n; ++i) printf("%d\n", i); } void nth(int n) { printf("%d\n, n); } Notice they both are having similar signature. So we can create function pointer which would be able to point both the functions . It can be done by the method given below.
An object of type std::function<Signature> behaves pretty much like a function pointer pointing to a function with the signature Signature. A default constructed std::function<Signature> just doesn't point at any function, yet. The key difference between std::function<Signature> and a function pointer Signature* is that you can have some state in form of a function object in std::function<Signature>.
To use an object of this type you'll need to initialize it with a suitable function, e.g.
#include <functional>
typedef std::function<unsigned int(const std::string&)> HashFunction;
struct Hash {
unsigned int operator()(std::string const& s) const {
return 0; // this is a pretty bad hash! a better implementation goes here
}
};
int main() {
HashFunction hash{ Hash() };
hash("hello");
}
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