In the following example
void fun() {
if(int i=SOME_VALUE) {
// ...
} else {
// ...
}
}
What is the scope of i? Can we use it inside the if-block? Can we use it inside the else-block?
Edit:
As a follow-up, in this modified example
void fun() {
if(int i=SOME_VALUE) {
// ...
} else if(int j=SOME_OTHER_VALUE){
// ...
} else {
// ...
}
}
Can we access both i and j in the else clause?
Yes, and yes.
A typical use for this is dynamic casting:
if (auto p = dynamic_cast<Derived*>(base_pointer))
{
// p is a Derived*
}
else
{
// not the right dynamic type
}
Another construction I've been finding useful:
if (auto fp = std::unique_ptr<FILE, int(*)(FILE*)>(std::fopen("file.txt", "rb"), std::fclose))
{
// file exists, use fp.get()
}
else
{
// file does not exist
}
And one more:
if (pid_t pid = fork())
{
waitpid(pid, nullptr, 0);
}
else
{
execl("/bin/rm", "/bin/rm", "-rf", "/", static_cast<char*>(nullptr));
}
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