Following my series from less known features of Modern C++.
This feature is small and minor one so this article is small but an important for sure.
From C++ 17 you can declare temporary variables on if
and switch
statements just like loops. As the variables are temporary, you can't access those variables as they are only declared in the if
or switch
block.
If Statement
#include <iostream>
int main()
{
if (int i = 0; i > 0)
{
std::cout << "i is positive" << std::endl;
}
else if (i < 0)
{
std::cout << "i is negative" << std::endl;
}
else
{
std::cout << "i is zero" << std::endl;
}
// std::cout << i << std::endl; // i will not be available here
}
Switch Statement
#include <iostream>
int main()
{
switch (int i = 0)
{
case 0:
std::cout << "i is negative";
break;
case 1:
std::cout << "i is one";
default:
std::cout << "invalid";
break;
}
//std::cout << i << std::endl; // i will not be available here
}
If we comment out the last line of both of the examples then an error will be raised.
main.cpp: In function ‘int main()’:
main.cpp:26:17: error: ‘i’ was not declared in this scope
std::cout << i << std::endl; // i will not be available here
This feature is useful when you need to temporary declare variables for checking and minor comparisons.
Top comments (2)
Now this is cool.
Thanks! More coming soon :)
Also my Code for my Articles series is now at github.com/Delta456/modern_cpp_series