C++ How to Program, 10/e

E.6 #error and #pragma Preprocessing Directives

The #error directive

• error tokens

prints an implementation-dependent message including the tokens specified in the directive. The tokens are sequences of characters separated by spaces. For example,

#error 1 - Out of range error

contains six tokens. In one popular C++ compiler, for example, when a #error directive is processed, the tokens in the directive are displayed as an error message, preprocessing stops and the program does not compile.

The #pragma directive

#pragma tokens

causes an implementation-defined action. A pragma not recognized by the implementation is ignored. A particular C++ compiler, for example, might recognize pragmas that enable you to take advantage of that compiler’s ...