Why I can't declare a std::string type in a switch/case box?

Here is the code.

Code:

int main(int argc, char* argv[]){ int i=2; switch (i) { case 0: cout<<0<<endl; break; case 1: string test=""; cout<<1<<endl; break; case 2: cout<<2<<endl; break; default: break; } return 0; }

as you can see, when declare a string test it reports errors

Quote:

main.cc: In function `int main(int, char**)':
main.cc:24: error: jump to case label
main.cc:21: error: crosses initialization of `std::string test'
main.cc:27: error: jump to case label
main.cc:21: error: crosses initialization of `std::string test'
main.cc:24: warning: destructor needed for `std::string test'
main.cc:24: warning: where case label appears here
main.cc:24: warning: (enclose actions of previous case statements requiring
destructors in their own scope.)
main.cc:27: warning: destructor needed for `std::string test'
main.cc:27: warning: where case label appears here
make: *** [main.o] Error 1

I don't understand the errors, what is "jump to case label" ?
why I "crosses initialization of `std::string test'" ?

Interestingly, if I put the declaration in a box, it's OK

Code:

int main(int argc, char* argv[]){ int i=2; switch (i) { case 0: cout<<0<<endl; break; case 1: { string test=""; } cout<<1<<endl; break; case 2: cout<<2<<endl; break; default: break; } return 0; }

That's the way to do it (whenever you need to declare variables in a case). Otherwise test would be in scope in the following cases too, but you could jump over the declaration (and construction) of it.

Interesting little corner of the language.

A switch case is the same as a labeled "goto" statement. You are not allowed to "goto" a location in a block following the construction point of a local variable, and you can't do it with a switch either.

The problem is, the string is still in scope at case 2. Each labeled section of a switch statement is NOT its own scope. So going to case 2 would bring the variable into scope even though it has not been constructed.

Placing it in a block creates a new scope, so that the variable's scope is limited to case 1.

EDIT: Some code to help clarify:

Code:

goto foo; std::string x; foo: std::cout << x << std::endl;

The declaration brings a variable 'x' into scope -- however, the line itself, which constructs the variable, is skipped by the goto statement. So x is used without being initialized. The same thing is happening here.