Question

What does the C++ language definition promise about casting a char to bool then back to char again?

char original = 255;
bool next = original;
char final = next;

Also, what do most compilers do in this case beyond what the language guarantees?

Answer 1

This will give a value of zero or one, depending on whether the original value was zero or non-zero.

Converting to bool gives a value of true or false:

4.12 A zero value, null pointer value, or null member pointer value is converted to false;
any other value is converted to true.

Converting back to char converts false to zero, and true to one:

4.7/4 If the source type is bool, the value false is converted to zero and
the value true is converted to one.