Nios II Software Developer’s Handbook中

 Nios II IDE
The Nios II integrated development environment (IDE) is the software
development graphical user interface (GUI) for the Nios II processor. All
software development tasks can be accomplished within the Nios II IDE,
including editing, building, and debugging programs. The Nios II IDE is
the window through which all other tools can be launched.
The Nios II IDE is based on the popular Eclipse IDE framework and the
Eclipse C development toolkit (CDT) plug-ins. The Nios II IDE is a thinuser
interface that manipulates other tools behind the scenes, shields you
from the details of command-line tools, and presents a unified
development environment. If necessary, software development processes
can be scripted and executed independently of the GUI.
GNU Tool Chain
The Nios II compiler tool chain is based on the standard GNU GCC
compiler, assembler, linker, and makefile facilities.
For more information on GNU, see www.gnu.org.

中可以看到

The Nios II compiler tool chain is based on the standard GNU GCC
而发行的GNU C 编译器(GCC)是一个全功能的ANSI C 兼容编译器

所以和一般使用的标准ASNI C是一样的。