在使用clang ++的Mac os上编译源代码时，出现此警告标志。 完整的编译选项
-Wall -Wextra -Wcast-align -Wfloat-equal -Wformat=2 -Wlogical-op -Wno-missing-field-initializers -Wno-old-style-cast -Wno-sign-compare -Wno-sign-conversion -Wno-write-strings -Wreturn-type -Werror=return-type -Werror=uninitialized -Wunreachable-code -Wno-keyword-macro -Wno-reserved-id-macro -Wno-unused-const-variable $1 $2 $3