总结了一下，主要有几点，欢迎指正。
1、cout对应于标准输出流
cerr对应于标准错误流
2、cout可以重定向，cerr不可以。
3、cout要分配缓冲，cerr不用，所以从理论上来说，cerr输出要比cout要快。
4、cout和cerr默认都是标准输出设备：显示器.
英文表述是：
cout:
The cout object corresponds to the standard output stream. By default, this stream is associated with the standard output device, typically a monitor. The wcout object is similar but works with the wchar_t type.
cerr:
The cerr object corresponds to the standard error stream, which you can use for displaying error messages. By default, this stream is associated with the standard output device, typically a monitor, and the stream is unbuffered. This means that information is sent directly to the screen, without waiting for a buffer to fill or for a newline character. The wcerr object is similar but works with the wchar_t type.