simple c++ question about switch and "cross-initialization" error?

Question

simple c++ question about switch and "cross-initialization" error?

Answer 1

RE:

simple c++ question about switch and "cross-initialization" error?

switch (0) {

case 1:

int b = 0;

break;

default:

break;

}



This gives "error: jump to case label" and "error: cross initialization of 'int b.'" What does this mean?

Ways to remove error:

1) change line 3 into "int b; b = 0;"

2) put {} around...

Answer 2

I just moved the declaration for "b" outside the switch statement.



#include

using namespace std;



int main()

{

int b;



switch (0)

{

case 1:

b = 0;

break;



default:

break;

}



system ("PAUSE");



return 0;

}

Answer 3

The reason is that such jump is a scoping violation. C++ standard ISO 14882:2003 says this in paragraph 6.7.3



It is possible to transfer into a block, but not in a way that bypasses declarations with initialization. A program that jumps (77) from a point where a local variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has POD type (3.9) and is declared without an initializer (8.5).



77) The transfer from the condition of a switch statement to a case label is considered a jump in this respect.





so in your question, option (1) declares a POD variable without an initializer, which is expressly permitted, option (2) makes a new block, which ends its scope before the next case label, and thus you're no longer jumping into scope, and option (3) makes it impossible to jump into the block *after* the initialization because there are no case labels after default:.