http://www.mingw.org/Welcome_to_MinGW...上有说明
MinGW compilers provide access to the functionality of the Microsoft C runtime and some language-specific runtimes. MinGW, being Minimalist, does not, and never will, attempt to provide a POSIX runtime environment for POSIX application deployment on MS-Windows.
所以如果你要使用posix标准的一些api,诸如fork之类,就得使用cygwin中的gcc(如果你是在windows上开发),因为MinGW只会使用M$提供的功能。