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Edit summary for version 15 :

Version 14

Version 15

Idiom #59 Write to standard error stream

Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").

Idiom #59 Write to standard error stream

Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").

Imports
import "dart:io";
Code
stderr.write("$x is negative");
Doc URL
https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:io#id_stderr