blocks|key|110185|text|对于Swift+4.x：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|110186|import+Darwin
fputs("hello+from+libc\n",+stderr)|code-block|syntax|javascript|110187|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|$]]

For Swift 4.x:

<pre><code>import Darwin
fputs("hello from libc\n", stderr)
</code></pre>

blocks|key|110214|text|这是一个修改自https://gist.github.com/algal/0a9aa5a4115d86d5cc1de7ea6d06bd91的Swift+3代码片段。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|110215|import+Foundation

var+standardError+=+FileHandle.standardError

extension+FileHandle:+TextOutputStream+{
++public+func+write(_+string:+String)+{
++++let+data+=+Data(string.utf8)
++++self.write(data)
++}
}

print("I+am+printed+to+stderr",+to:+&standardError)|code-block|syntax|javascript|110216|entityMap|0|LINK|mutability|MUTABLE|url|https://gist.github.com/algal/0a9aa5a4115d86d5cc1de7ea6d06bd91^0|7|1Q|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]]]]

Here is a Swift 3 snippet modified from <a href="https://gist.github.com/algal/0a9aa5a4115d86d5cc1de7ea6d06bd91" rel="nofollow noreferrer">https://gist.github.com/algal/0a9aa5a4115d86d5cc1de7ea6d06bd91</a>.
<pre><code>import Foundation

var standardError = FileHandle.standardError

extension FileHandle: TextOutputStream {
 public func write(_ string: String) {
 let data = Data(string.utf8)
 self.write(data)
 }
}

print(&quot;I am printed to stderr&quot;, to: &amp;standardError)
</code></pre>

blocks|key|110083|text|这可能是一种更好的方法，但您可以使用NSFileHandle|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|110084|import+Foundation

//+Create+a+file+handle+to+work+with
let+stderr+=+NSFileHandle.fileHandleWithStandardError()

//+Build+up+a+string;+whatever+you+want
let+stuff+=+"something"
let+something+=+"I'm+a+string+with+\(stuff)+in+it\n"

//+Write+it
stderr.writeData(something.dataUsingEncoding(NSUTF8StringEncoding))|code-block|syntax|javascript|110085|entityMap^0|I|C|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

May be a better way to do it, but you can use <code>NSFileHandle</code>:

<pre><code>import Foundation

// Create a file handle to work with
let stderr = NSFileHandle.fileHandleWithStandardError()

// Build up a string; whatever you want
let stuff = "something"
let something = "I'm a string with \(stuff) in it\n"

// Write it
stderr.writeData(something.dataUsingEncoding(NSUTF8StringEncoding))
</code></pre>

blocks|key|4616409|text|实际上不是一个单独的答案，但在Rob+Napier的答案之上，我们可以创建一个类似stderr的对象，这样当苹果将stderr作为OutputStreamType提供时，就不需要做太多的更改|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4616410|import+Foundation

class+StandardErrorOutputStream:+OutputStreamType+{
++func+write(string:+String)+{
++++let+stderr+=+NSFileHandle.fileHandleWithStandardError()
++++stderr.writeData(string.dataUsingEncoding(NSUTF8StringEncoding))
++}
}

var+mx_stderr+=+StandardErrorOutputStream()

println("on-stdout")
println("on-stderr",+&mx_stderr)|code-block|syntax|javascript|4616411|编辑:从2015年8月26日Xcode+7+Beta+6开始，您需要toStream:参数名称，如下所示：|4616412|println("on-stderr",+toStream:&mx_stderr)|4616413|entityMap^0|1T|G|0|0|Y|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

Not really a separate answer, but building on top of Rob Napier's answer, we can create a stderr like object so that there is not much to change when Apple comes around to providing stderr as an <code>OutputStreamType</code>:

<pre><code>import Foundation

class StandardErrorOutputStream: OutputStreamType {
 func write(string: String) {
 let stderr = NSFileHandle.fileHandleWithStandardError()
 stderr.writeData(string.dataUsingEncoding(NSUTF8StringEncoding))
 }
}

var mx_stderr = StandardErrorOutputStream()

println("on-stdout")
println("on-stderr", &amp;mx_stderr)
</code></pre>

EDIT: As of 8/26/2015, Xcode 7 Beta 6, you need the <code>toStream:</code> parameter name, like so:

<pre><code>println("on-stderr", toStream:&amp;mx_stderr)
</code></pre>

blocks|key|110271|text|Swift+4，类似于Ryan的解决方案，但没有扩展FileHandle，而是创建了一个新的结构，它还允许您创建一个特定于StdErr的类，并避免全局。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|110272|struct+StandardErrorOutputStream:+TextOutputStream+{
++++let+stderr+=+FileHandle.standardError

++++func+write(_+string:+String)+{
++++++++guard+let+data+=+string.data(using:+.utf8)+else+{
++++++++++++fatalError()+//+encoding+failure:+handle+as+you+wish
++++++++}
++++++++stderr.write(data)
++++}
}|code-block|syntax|javascript|110273|使用示例：|110274|do+{+
++++try+somethingThatMightFail()+
}+catch+let+error+{
++++var+errStream+=+StandardErrorOutputStream()
++++print("\(error)",+to:+&errStream)
++++exit(EXIT_FAILURE)
}|110275|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|$]]

Swift 4, similar to Ryan's solution but instead of extending the FileHandle, created a new struct which also lets you create a StdErr specific class and avoids the global.
<pre><code>struct StandardErrorOutputStream: TextOutputStream {
 let stderr = FileHandle.standardError

 func write(_ string: String) {
 guard let data = string.data(using: .utf8) else {
 fatalError() // encoding failure: handle as you wish
 }
 stderr.write(data)
 }
}
</code></pre>
Usage example:
<pre><code>do { 
 try somethingThatMightFail() 
} catch let error {
 var errStream = StandardErrorOutputStream()
 print(&quot;\(error)&quot;, to: &amp;errStream)
 exit(EXIT_FAILURE)
}
</code></pre>

blocks|key|4616544|text|Xcode+11.3%2B和Swift+5.1%2B|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4616545|扩展名：|4616546|final+class+StandardErrorOutputStream:+TextOutputStream+{
++++func+write(_+string:+String)+{
++++++++FileHandle.standardError.write(Data(string.utf8))
++++}
}|code-block|syntax|javascript|4616547|用法：|4616548|var+outputStream+=+StandardErrorOutputStream()
print("Error!",+to:+&outputStream)|4616549|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Xcode 11.3+ and Swift 5.1+
Extension:
<pre><code>final class StandardErrorOutputStream: TextOutputStream {
 func write(_ string: String) {
 FileHandle.standardError.write(Data(string.utf8))
 }
}
</code></pre>
Usage:
<pre><code>var outputStream = StandardErrorOutputStream()
print(&quot;Error!&quot;, to: &amp;outputStream)
</code></pre>

blocks|key|4616591|text|@RobNapier建议的解决方案的精简和现代化版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4616592|"A+line+of+text"
++++.data(using:+.utf8)
++++.map(FileHandle.standardError.write)|code-block|syntax|javascript|4616593|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|$]]

A condensed and modernized version of @RobNapiers suggested solution:
<pre><code>&quot;A line of text&quot;
 .data(using: .utf8)
 .map(FileHandle.standardError.write)
</code></pre>

I'm trying to make a command line tool for OS X with Xcode 6 and the new Swift language. How can I send output to stderr? Is this done with println?

How can I output to STDERR with Swift?

命令行工具

Swift

Xcode

我正在尝试用Xcode6和新的Swift语言为OS X制作一个命令行工具。如何将输出发送到stderr？这是用println完成的吗？

问如何使用Swift输出到STDERR？
EN

回答 7

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问如何使用Swift输出到STDERR？EN

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问如何使用Swift输出到STDERR？
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