12. Statements

impossible conditions

Use the construct assert (0); when an impossible condition is detected, i.e., for an impossible default: case in a switch statement.

switch statements

Always include a default case in a switch, even if it is a failing assertion or an empty statement.

labels and statements

A label, both goto targets and cases, must be followed by a statement, even if that is an empty statement. This is required by the ANSI standard.

infinite loops

Write infinite loops with for (;;).

goto

There are three acceptable uses for goto, two of them related:

• A jump to an error recovery and unsuccessful exit routine at the end of the function, labeled error:. The code so labeled is only executed to handle an error or exception.

• A jump to a routine to generally finish and exit, at the end of a function and labeled as done:. The labeled code is executed whether the function is successful or not. Most functions of this type have a Boolean local variable named success used to indicate whether the function's work was successful.

• A jump out of nested loops or out of a loop containing a switch.

Many error recovery actions of the first two types can be avoided by use of pools. The third type is rarely necessary.

common case following if

In an if/else construct, put the common case after the if, not the else.

multi-statement macros

If a macro's definition contains multiple statements, enclose them with do { ... } while (0) to allow them to work properly in all syntactic circumstances.