diff options
Diffstat (limited to 'system/doc/reference_manual/macros.xml')
| -rw-r--r-- | system/doc/reference_manual/macros.xml | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/system/doc/reference_manual/macros.xml b/system/doc/reference_manual/macros.xml index 42ea639b54..350bb1d123 100644 --- a/system/doc/reference_manual/macros.xml +++ b/system/doc/reference_manual/macros.xml @@ -234,6 +234,53 @@ or </section> <section> + <title>-error() and -warning() directives</title> + + <p>The directive <c>-error(Term)</c> causes a compilation error.</p> + + <p><em>Example:</em></p> + <code type="none"> +-module(t). +-export([version/0]). + +-ifdef(VERSION). +version() -> ?VERSION. +-else. +-error("Macro VERSION must be defined."). +version() -> "". +-endif.</code> + + <p>The error message will look like this:</p> + + <pre> +% <input>erlc t.erl</input> +t.erl:7: -error("Macro VERSION must be defined.").</pre> + + <p>The directive <c>-warning(Term)</c> causes a compilation warning.</p> + + <p><em>Example:</em></p> + <code type="none"> +-module(t). +-export([version/0]). + +-ifndef(VERSION). +-warning("Macro VERSION not defined -- using default version."). +-define(VERSION, "0"). +-endif. +version() -> ?VERSION.</code> + + <p>The warning message will look like this:</p> + + <pre> +% <input>erlc t.erl</input> +t.erl:5: Warning: -warning("Macro VERSION not defined -- using default version.").</pre> + + <p>The <c>-error()</c> and <c>-warning()</c> directives were added + in OTP 19.</p> + + </section> + + <section> <title>Stringifying Macro Arguments</title> <p>The construction <c>??Arg</c>, where <c>Arg</c> is a macro argument, is expanded to a string containing the tokens of @@ -253,5 +300,6 @@ io:format("Call ~s: ~w~n",["you : function ( 2 , 1 )",you:function(2,1)]).</code <p>That is, a trace output, with both the function called and the resulting value.</p> </section> + </chapter> |