Why compiler allows narrowing conversions

Question

Can anyone please explain to me, why the compiler allows initialize variables of built-in type if the initializer might lead to the loss of information?

For example

Answer 1

One of the features of initializer lists is that narrowing conversions are not allowed. But the language definition doesn't distinguish between warnings and errors; when code is ill-formed it requires "a diagnostic", which is defined as any message from a set of implementation-defined messages. Warnings satisfy this requirements. That's the mechanism for non-standard extensions: having issued a warning, the compiler is free to do anything it wants to, including compiling something according to implementation-specific rules.

Answer 2

You can set the compiler flag to flag all warnings as error. In that case only it will stop you from doing like that. Otherwise it will only be a warning.

Answer 3

This issue has been coming up lately. With gcc-4.7 a command line switch turns on the required behaviour:

g++ -Werror=narrowing ...