weird output when I use pthread and printf

Question

I write a program using pthread.

Environment:windows 7 , CYGWIN_NT-6.1 i686 Cygwin , gcc (GCC) 4.5.3

The source code

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Answer 1

Just because a function is thread-safe, it doesn't mean it's atomic.

In your case, if you want to ensure that your output don't get interleaved, you need to use a mutex to ensure that only one thread calls printf at a time.