查找g++文档的方法

http://www.gnu.org/

-> Software(http://www.gnu.org/software/software.html)

->搜索 "gcc"(http://www.gnu.org/software/gcc/)

->右侧 "Manual" (https://gcc.gnu.org/onlinedocs/)

->找到你想查看的版本，比如 : GCC 5.2 Manual (https://gcc.gnu.org/onlinedocs/gcc-5.2.0/gcc/)

->搜索 "GCC Command Options" (https://gcc.gnu.org/onlinedocs/gcc-5.2.0/gcc/index.html#toc_Invoking-GCC)

->搜索 "Option Summary"(https://gcc.gnu.org/onlinedocs/gcc-5.2.0/gcc/Option-Summary.html#Option-Summary)