E.6. #error and #pragma Preprocessing Directives
The #error directive
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
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 ...