blocks|key|1281911|text|标准输入的readLineSync()方法允许从控制台捕获字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1281912|import+'dart:convert';
import+'dart:io';

void+main()+{
++print('1+%2B+1+=+...');
++var+line+=+stdin.readLineSync(encoding:+utf8);
++print(line?.trim()+==+'2'+?+'Yup!'+:+'Nope+:(');
}|code-block|syntax|javascript|1281913|旧版本：|1281914|import+'dart:io';

main()+{
++++print('1+%2B+1+=+...');
++++var+line+=+stdin.readLineSync(encoding:+Encoding.getByName('utf-8'));
++++print(line.trim()+==+'2'+?+'Yup!'+:+'Nope+:(');
}|1281915|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The readLineSync() method of stdin allows to capture a String from the console:
<pre class="lang-dart prettyprint-override"><code>import 'dart:convert';
import 'dart:io';

void main() {
 print('1 + 1 = ...');
 var line = stdin.readLineSync(encoding: utf8);
 print(line?.trim() == '2' ? 'Yup!' : 'Nope :(');
}
</code></pre>
Old version:
<pre class="lang-dart prettyprint-override"><code>import 'dart:io';

main() {
 print('1 + 1 = ...');
 var line = stdin.readLineSync(encoding: Encoding.getByName('utf-8'));
 print(line.trim() == '2' ? 'Yup!' : 'Nope :(');
}
</code></pre>

blocks|key|3006010|text|以下代码应该是从标准输入读取输入的最新dart代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3006011|import+'dart:async';
import+'dart:io';
import+'dart:convert';

void+main()+{
++readLine().listen(processLine);
}

Stream<String>+readLine()+=>+stdin
++++.transform(utf8.decoder)
++++.transform(const+LineSplitter());

void+processLine(String+line)+{
++print(line);
}|code-block|syntax|javascript|3006012|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The following should be the most up to date dart code to read input from stdin.

<pre class="lang-dart prettyprint-override"><code>import 'dart:async';
import 'dart:io';
import 'dart:convert';

void main() {
 readLine().listen(processLine);
}

Stream&lt;String&gt; readLine() =&gt; stdin
 .transform(utf8.decoder)
 .transform(const LineSplitter());

void processLine(String line) {
 print(line);
}
</code></pre>

blocks|key|3006048|text|import+'dart:io';

void+main(){
++stdout.write("Enter+your+name+:+");
++var+name+=+stdin.readLineSync();
++stdout.write(name);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3006049|输出|unstyled|3006050|Enter+your+name+:+Jay
Jay|3006051|默认情况下，readLineSync()将输入作为字符串。但是如果你想要整数输入，那么你必须使用parse()或者tryparse()。|3006052|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>import 'dart:io';

void main(){
 stdout.write("Enter your name : ");
 var name = stdin.readLineSync();
 stdout.write(name);
}
</code></pre>

Output

<pre><code>Enter your name : Jay
Jay
</code></pre>

By default readLineSync() takes input as string. But If you want integer input then you have to use parse() or tryparse().

blocks|key|3005976|text|如果像StringInputStream这样的M3+dart类被Stream所取代，可以尝试这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3005977|import+'dart:io';
import+'dart:async';

void+main()+{
++print("Please,+enter+a+line+\n");
++Stream+cmdLine+=+stdin
++++++.transform(new+StringDecoder())
++++++.transform(new+LineTransformer());

++StreamSubscription+cmdSubscription+=+cmdLine.listen(
++++(line)+=>+print('Entered+line:+$line+'),
++++onDone:+()+=>+print('+finished'),
++++onError:+(e)+=>+/*+Error+on+input.+*/);


}|code-block|syntax|javascript|3005978|entityMap|0|LINK|mutability|MUTABLE|url|http://api.dartlang.org/docs/releases/latest/dart_async/Stream.html^0|W|6|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

With M3 dart classes like StringInputStream are replaced with <a href="http://api.dartlang.org/docs/releases/latest/dart_async/Stream.html" rel="nofollow">Stream</a>, try this:

<pre class="lang-dart prettyprint-override"><code>import 'dart:io';
import 'dart:async';

void main() {
 print("Please, enter a line \n");
 Stream cmdLine = stdin
 .transform(new StringDecoder())
 .transform(new LineTransformer());

 StreamSubscription cmdSubscription = cmdLine.listen(
 (line) =&gt; print('Entered line: $line '),
 onDone: () =&gt; print(' finished'),
 onError: (e) =&gt; /* Error on input. */);


}
</code></pre>

blocks|key|3006165|text|从Dart+2.12开始，启用了空安全，stdin.readLineSync()现在返回String?而不是String。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3006166|这显然让很多人感到困惑。我强烈建议阅读https://dart.dev/null-safety/understanding-null-safety来理解空安全的含义。|3006167|特别是对于stdin.readLineSync()，您可以通过首先检查null来解决这个问题，对于局部变量，它会自动将String?提升为String。下面是一些示例：|3006168|//+Read+a+line+and+try+to+parse+it+as+an+integer.
String?+line+=+stdin.readLineSync();
if+(line+!=+null)+{
++int?+num+=+int.tryParse(line);+//+No+more+error+about+`String?`.
++if+(num+!=+null)+{
++++//+Do+something+with+`num`...
++}
}|code-block|syntax|javascript|3006169|//+Read+lines+from+`stdin`+until+EOF+is+reached,+storing+them+in+a+`List<String>`.
var+lines+=+<String>[];
while+(true)+{
++var+line+=+stdin.readLineSync();
++if+(line+==+null)+{
++++break;
++}
++lines.add(line);+//+No+more+error+about+`String?`.
}|3006170|//+Read+a+line.++If+EOF+is+reached,+treat+it+as+an+empty+string.
String+line+=+stdin.readLineSync()+??+'';|3006171|请注意，您不应该盲目地使用+do+stdin.readLineSync()!。readLineSync返回一个String?是有原因的:当没有更多的输入时，它返回null。使用null+assertion+operator+(!)是在请求运行时异常。|3006172|entityMap|0|LINK|mutability|MUTABLE|url|https://dart.dev/null-safety/understanding-null-safety|1|https://dart.dev/null-safety/understanding-null-safety#null-assertion-operator^0|K|K|18|7|1I|6|0|J|1I|0|0|5|K|Z|4|1N|7|1X|6|0|0|0|0|H|L|13|C|1J|7|29|4|35|1|2G|N|1|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1B|8|@]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|H|3|I|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|1O|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|L|7|1P|8|@]|D|@]|E|$M|N]]|$1|Q|3|R|5|L|7|1Q|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1R|8|@$9|1S|A|1T|B|C]|$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]|$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]]|D|@$9|22|A|23|1|24]]|E|$]]|$1|U|3|-4|5|6|7|25|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]|12|$5|X|Y|Z|E|$10|13]]]]

As of Dart 2.12, null-safety is enabled, and <code>stdin.readLineSync()</code> now returns a <code>String?</code> instead of a <code>String</code>.
This apparently has been confusing a lot of people. I highly recommend reading <a href="https://dart.dev/null-safety/understanding-null-safety" rel="nofollow noreferrer">https://dart.dev/null-safety/understanding-null-safety</a> to understand what null-safety means.
For <code>stdin.readLineSync()</code> specifically, you can resolve this by checking for <code>null</code> first, which for local variables will automatically promote a <code>String?</code> to a <code>String</code>. Here are some examples:
<pre class="lang-dart prettyprint-override"><code>// Read a line and try to parse it as an integer.
String? line = stdin.readLineSync();
if (line != null) {
 int? num = int.tryParse(line); // No more error about `String?`.
 if (num != null) {
 // Do something with `num`...
 }
}
</code></pre>
<pre class="lang-dart prettyprint-override"><code>// Read lines from `stdin` until EOF is reached, storing them in a `List&lt;String&gt;`.
var lines = &lt;String&gt;[];
while (true) {
 var line = stdin.readLineSync();
 if (line == null) {
 break;
 }
 lines.add(line); // No more error about `String?`.
}
</code></pre>
<pre class="lang-dart prettyprint-override"><code>// Read a line. If EOF is reached, treat it as an empty string.
String line = stdin.readLineSync() ?? '';
</code></pre>
Note that you should not blindly do <code>stdin.readLineSync()!</code>. <code>readLineSync</code> returns a <code>String?</code> for a reason: it returns <code>null</code> when there is no more input. Using the <a href="https://dart.dev/null-safety/understanding-null-safety#null-assertion-operator" rel="nofollow noreferrer">null assertion operator</a> (<code>!</code>) is asking for a runtime exception.

blocks|key|2918055|text|请注意，在调用stdin.readLineSync()时，您的isolate/thread将被阻止，其他Future将不会完成。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2918056|如果您希望异步读取stdin+String行，以避免isolate/thread阻塞，则可以这样做：|2918057|import+'dart:async';
import+'dart:convert';
import+'dart:io';

///+[stdin]+as+a+broadcast+[Stream]+of+lines.
Stream<String>+_stdinLineStreamBroadcaster+=+stdin
++++.transform(utf8.decoder)
++++.transform(const+LineSplitter()).asBroadcastStream()+;

///+Reads+a+single+line+from+[stdin]+asynchronously.
Future<String>+_readStdinLine()+async+{
++var+lineCompleter+=+Completer<String>();

++var+listener+=+_stdinLineStreamBroadcaster.listen((line)+{
++++if+(!lineCompleter.isCompleted)+{
++++++lineCompleter.complete(line);
++++}
++});

++return+lineCompleter.future.then((line)+{
++++listener.cancel();
++++return+line+;
++});
}|code-block|syntax|javascript|2918058|entityMap^0|7|K|V|E|1G|6|0|9|5|F|6|Q|E|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|12|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|N|$]]

Note that while calling <code>stdin.readLineSync()</code> your <code>isolate/thread</code> will be blocked, no other <code>Future</code> will be completed.
If you want to read a <code>stdin</code> <code>String</code> line asynchronously, avoiding <code>isolate/thread</code> block, this is the way:
<pre class="lang-dart prettyprint-override"><code>import 'dart:async';
import 'dart:convert';
import 'dart:io';

/// [stdin] as a broadcast [Stream] of lines.
Stream&lt;String&gt; _stdinLineStreamBroadcaster = stdin
 .transform(utf8.decoder)
 .transform(const LineSplitter()).asBroadcastStream() ;

/// Reads a single line from [stdin] asynchronously.
Future&lt;String&gt; _readStdinLine() async {
 var lineCompleter = Completer&lt;String&gt;();

 var listener = _stdinLineStreamBroadcaster.listen((line) {
 if (!lineCompleter.isCompleted) {
 lineCompleter.complete(line);
 }
 });

 return lineCompleter.future.then((line) {
 listener.cancel();
 return line ;
 });
}

</code></pre>

blocks|key|1693725|text|您可以使用以下行从用户读取字符串：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1693726|String+str+=+stdin.readLineSync();|code-block|syntax|javascript|1693727|或以下行读取号|1693728|int+n+=+int.parse(stdin.readLineSync());|1693729|考虑以下示例：|1693730|import+'dart:io';+//+we+need+this+to+use+stdin
void+main()
{
++++//+reading+the+user+name
++++print("Enter+your+name,+please:+");
++++String+name+=+stdin.readLineSync();
++
++++//+reading+the+user+age
++++print("Enter+your+age,+please:+");
++++int+age+=+int.parse(stdin.readLineSync());
++
++++//+Printing+the+data
++++print("Hello,+$name!,+Your+age+is:+$age");
++
++/*+OR+print+in+this+way
+++*+stdout.write("Hello,+$name!,+Your+age+is:+$age");
+++*+*/
}|1693731|entityMap^0|D|3|0|0|6|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|T|$]]

You can use the following line to read a string from the user:
<pre><code>String str = stdin.readLineSync();
</code></pre>
OR the following line to read a number
<pre><code>int n = int.parse(stdin.readLineSync());
</code></pre>
Consider the following example:
<pre><code>import 'dart:io'; // we need this to use stdin
void main()
{
 // reading the user name
 print(&quot;Enter your name, please: &quot;);
 String name = stdin.readLineSync();
 
 // reading the user age
 print(&quot;Enter your age, please: &quot;);
 int age = int.parse(stdin.readLineSync());
 
 // Printing the data
 print(&quot;Hello, $name!, Your age is: $age&quot;);
 
 /* OR print in this way
 * stdout.write(&quot;Hello, $name!, Your age is: $age&quot;);
 * */
}
</code></pre>

blocks|key|1282180|text|所有这些基于异步API+readLine*()的解决方案都缺少语法糖，语法糖让你能够在没有同步阻塞的情况下做任何事情，但编写起来像同步代码。这甚至更直观地来自其他语言，在这些语言中，您可以编写同步执行的代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1282181|import+'dart:convert';
import+'dart:io';

Future<void>+main()+async+{
++var+lines+=+stdin.transform(utf8.decoder).transform(const+LineSplitter());
++
++await+for+(final+l+in+lines)+{
++++print(l);
++}
++print("done");
}|code-block|syntax|javascript|1282182|这里的关键要点是使用async和await|offset|length|style|CODE|1282183|方法上的|1282184|async是必需的，因为您正在使用await).|unordered-list-item|1282185|与异步await进行接口。Stream是在Future上执行“类同步”代码的语法(对应的API语法就是API|1282186|可以将await看作是通过让下面的代码在可以处理的情况下执行来为您“解开”Stream/Future。现在你不再阻塞你的主线程(Isolate)来完成这项工作。|1282187|有关详细信息，请参阅async/await上的Dart+codelab。|1282188|(附注:为async函数声明任何返回值的正确方法是将其包装在Future中，因此此处为Future<void>。)|1282189|entityMap|0|LINK|mutability|MUTABLE|url|https://dart.dev/codelabs/async-await^0|0|0|A|5|G|5|0|0|0|5|H|5|0|3|5|D|6|L|6|0|3|5|11|6|18|6|1S|7|0|N|C|0|0|5|5|U|6|17|C|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|19|8|@$I|1A|J|1B|K|L]|$I|1C|J|1D|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|1E|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1F|8|@$I|1G|J|1H|K|L]|$I|1I|J|1J|K|L]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1K|8|@$I|1L|J|1M|K|L]|$I|1N|J|1O|K|L]|$I|1P|J|1Q|K|L]]|9|@]|A|$]]|$1|T|3|U|5|6|7|1R|8|@$I|1S|J|1T|K|L]|$I|1U|J|1V|K|L]|$I|1W|J|1X|K|L]|$I|1Y|J|1Z|K|L]]|9|@]|A|$]]|$1|V|3|W|5|6|7|20|8|@]|9|@$I|21|J|22|1|23]]|A|$]]|$1|X|3|Y|5|6|7|24|8|@$I|25|J|26|K|L]|$I|27|J|28|K|L]|$I|29|J|2A|K|L]]|9|@]|A|$]]|$1|Z|3|-4|5|6|7|2B|8|@]|9|@]|A|$]]]|10|$11|$5|12|13|14|A|$15|16]]]]

All these async API readLine*() based solutions miss the syntactic sugar which gives you the ability to do everything without synchronous blocking, but written like synchronous code. This is even more intuitive coming from other languages where you write code to execute synchronously:
<pre><code>import 'dart:convert';
import 'dart:io';

Future&lt;void&gt; main() async {
 var lines = stdin.transform(utf8.decoder).transform(const LineSplitter());
 
 await for (final l in lines) {
 print(l);
 }
 print(&quot;done&quot;);
}
</code></pre>
The key takeaway here is to make use of <code>async</code> and <code>await</code>:
<ul>
<li><code>async</code> on your method is required, as you're using <code>await</code> to interface with asynchronous API calls</li>
<li><code>await for</code> is the syntax for doing &quot;synchronous-like&quot; code on a <code>Stream</code> (the corresponding syntax for a <code>Future</code> is just <code>await</code>).</li>
</ul>
Think of <code>await</code> like &quot;unwrapping&quot; a <code>Stream</code>/<code>Future</code> for you by making the following code execute once something is available to be handled. Now you're no longer blocking your main thread (<code>Isolate</code>) to do the work.
For more information, see the <a href="https://dart.dev/codelabs/async-await" rel="nofollow noreferrer">Dart codelab</a> on async/await.
(Sidenote: The correct way to declare any return value for an <code>async</code> function is to wrap it in a <code>Future</code>, hence <code>Future&lt;void&gt;</code> here.)

How do I read console input from <code>stdin</code> in Dart?

Is there a <code>scanf</code> in Dart?

How do I read console input / stdin in Dart?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何在Dart中读取来自stdin的控制台输入？Dart中有scanf吗？

问如何在Dart中读取控制台输入/标准输入？
EN

回答 8

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问如何在Dart中读取控制台输入/标准输入？EN

回答 8

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问如何在Dart中读取控制台输入/标准输入？
EN