System.out、stdout 和 cout 在 Java、C 和 C++ 中分别是完全相同的东西吗？

为什么同一事物有三个不同的名称(尤其是当 C、C++ 和 Java 有很多共同点时)？

此外，我知道它们的用途，但我的意思是，它们到底是什么？

最佳答案

cout本质上与 stdout 相同但不同的是 cout类型为 ostream (这实际上意味着您可以使用 << 输入格式化数据或使用 write 方法输入未格式化数据。

stdout附加到文件描述符(标准输出是 FILE* )。 stdout文件描述符是 1 .因为它返回对文件描述符的引用，所以可以在 fputs 中使用和 fprintf .

Java System.out本质上就像 stdout (它使用 java.io.FileDescriptor 和句柄 1 )并传递给 FileOutputStream最后包裹在里面 BufferedOutputStream .

这就是java.lang.System已初始化:

 /**
     * Initialize the system class.  Called after thread initialization.
     */
    private static void initializeSystemClass() {
    props = new Properties();
    initProperties(props);
    sun.misc.Version.init();

        // Workaround until DownloadManager initialization is revisited.
        // Make JavaLangAccess available early enough for internal
        // Shutdown hooks to be registered
        setJavaLangAccess();

        // Gets and removes system properties that configure the Integer
        // cache used to support the object identity semantics of autoboxing.
        // At this time, the size of the cache may be controlled by the
        // vm option -XX:AutoBoxCacheMax=<size>.
        Integer.getAndRemoveCacheProperties();

    // Load the zip library now in order to keep java.util.zip.ZipFile
    // from trying to use itself to load this library later.
    loadLibrary("zip");

    FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
    FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
    FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
    setIn0(new BufferedInputStream(fdIn));
    setOut0(new PrintStream(new BufferedOutputStream(fdOut, 128), true));
    setErr0(new PrintStream(new BufferedOutputStream(fdErr, 128), true));

    // Setup Java signal handlers for HUP, TERM, and INT (where available).
        Terminator.setup();

        // Initialize any miscellenous operating system settings that need to be
        // set for the class libraries. Currently this is no-op everywhere except
        // for Windows where the process-wide error mode is set before the java.io
        // classes are used.
        sun.misc.VM.initializeOSEnvironment();

    // Set the maximum amount of direct memory.  This value is controlled
    // by the vm option -XX:MaxDirectMemorySize=<size>.  This method acts
    // as an initializer only if it is called before sun.misc.VM.booted().
    sun.misc.VM.maxDirectMemory();

    // Set a boolean to determine whether ClassLoader.loadClass accepts
    // array syntax.  This value is controlled by the system property
    // "sun.lang.ClassLoader.allowArraySyntax".  This method acts as
    // an initializer only if it is called before sun.misc.VM.booted().
    sun.misc.VM.allowArraySyntax();

    // Subsystems that are invoked during initialization can invoke
    // sun.misc.VM.isBooted() in order to avoid doing things that should
    // wait until the application class loader has been set up.
    sun.misc.VM.booted();

        // The main thread is not added to its thread group in the same
        // way as other threads; we must do it ourselves here.
        Thread current = Thread.currentThread();
        current.getThreadGroup().add(current);
    }

FileDescriptor.out是:

/**
 * A handle to the standard output stream. Usually, this file
 * descriptor is not used directly, but rather via the output stream
 * known as <code>System.out</code>.
 * @see     java.lang.System#out
 */
public static final FileDescriptor out = standardStream(1);

来源:

• cout
• stdout
• Wikipedia在 System.out , cout和 stdout

关于java - System.out、stdout 和 cout 是一回事吗？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/3873445/