Changing variable in c-CodePudding

I started learning C and I made a simple thing like printing variables etc, but I wanted to make a new value on a variable like in Python:

test = "hello world"
print(test)
test = 5
print(test   6)

So I had this:

string test = "hello world";
cout << test << "\n";

And now I wanted to assign a number to test, so I used int test = 5;, but I got an error:

redefinition of 'test' with a different type

Is it possible to assign a new type to a variable somehow?

CodePudding user response：

is it possible to assign a new type to a variable somehow?

A new type, no. C is a statically typed language. Variable types are specified at compile-time and cannot change at runtime.

For what you are asking, the closest thing available is std::variant in C 17 and later, which is a fixed class type that can hold different kinds of values at runtime, eg:

#include <iostream>
#include <string>
#include <variant>

using myVariant = std::variant<int, std::string>;

void print(const myVariant &v)
{
    std::visit([](const auto &x) { std::cout << x; }, v);
    std::cout << "\n";
}

int main()
{
    myVariant test;
    test = "hello world";
    print(test);
    test = 5;
    print(test);
    return 0;
}

Online Demo

CodePudding user response：

In C 17 and newer, std::variant is a type that can be used to store multiple different types of data. Though you'll have to do a bit of finagling with visitors to get the polymorphic print you know from Python.

#include <variant>
#include <string>
#include <iostream>

struct PrintVisitor {
  template <typename T>
  void operator()(const T& arg) {
    std::cout << arg << std::endl;
  }
};

int main() {
  std::variant<std::string, int> test = "hello world";
  std::visit(PrintVisitor(), test);
  test = 5;
  std::visit(PrintVisitor(), test);
}