Le 14/01/13 02:50, TONGARI a écrit :
2013/1/14 Brian Ravnsgaard Riis <brian@ravnsgaard.net>
Den Sun, 13 Jan 2013 20:30:14 +0100 skrev Vicente J. Botet Escriba < vicente.botet@wanadoo.fr>:
[snip]
Of course in order to be really structired the jumping to the underlying
label should be forbiden (by the compiler), but I don't think that a preprocessor solution could take care of this. So the following not desired and not structured code could compile even if we would like an compile error.
BOOST_NAMED_BLOCK(L) { // ... } // [1] //... BOOST_BREAK(L); // go to [1]
So, the underlying idea is to get something like "break" and "continue" to work inside any "named" block, not just loops? If so (as you demonstrate above) I'm fairly certain a correct solution cannot be implemented using just the preprocessor.
Hey guys,
Please try the code attached and see the error message that your compiler gives. It DOES avoid the ill-formed code like that to compile.
Yeah. I was your macro forbid the access from outside the block. I though that the trick was used only to be able to add a label at the end of the block. But the use of the variable on the BREAK macro make it fail. Really clever. #define BOOST_SCOPE(name) \ if (const bool LABELED_SCOPE_##name = false){BOOST_BREAK(name); name##_end_scope:;} else #define BOOST_BREAK(name) \ (void)LABELED_SCOPE_##name; goto name##_end_scope I have tried int main() { BOOST_SCOPE(a2) { BOOST_BREAK(a2); cout << "123\n"; } BOOST_SCOPE(a1) { BOOST_BREAK(a2); cout << "123\n"; } return 0; } and here are the error for gcc darwin.compile.c++ ../../../bin.v2/libs/thread/test/test_so.test/darwin-4.7.2x/debug/threading-multi/test_so.o ../example/test_so.cpp: In function ‘int main()’: ../example/test_so.cpp:22:1: erreur: ‘LABELED_SCOPE_a2’ was not declared in this scope ../example/test_so.cpp:15:1: attention : jump to label ‘a2_end_scope’ [-fpermissive] ../example/test_so.cpp:22:1: attention : à partir d'ici [-fpermissive] ../example/test_so.cpp:15:1: erreur: skips initialization of ‘const bool LABELED_SCOPE_a2’ and clang clang-darwin.compile.c++ ../../../bin.v2/libs/thread/test/test_so.test/clang-darwin-3.2xl/debug/threading-multi/test_so.o ../example/test_so.cpp:22:7: error: use of undeclared identifier 'LABELED_SCOPE_a2' BOOST_BREAK(a2); ^ ../example/test_so.cpp:10:7: note: expanded from macro 'BOOST_BREAK' (void)LABELED_SCOPE_##name; goto name##_end_scope ^ <scratch space>:232:1: note: expanded from macro 'LABELED_SCOPE_' LABELED_SCOPE_a2 ^ Best, Vicente