gcc中的 -w -W和-Wall选项

 -Waddress 
 -Warray-bounds=1 (only with -O2) 
 -Wbool-compare 
 -Wbool-operation 
 -Wc++11-compat  
 -Wc++14-compat 
 -Wcatch-value (C++ and Objective-C++ only) 
 -Wchar-subscripts 
 -Wcomment 
 -Wduplicate-decl-specifier (C and Objective-C only) 
 -Wenum-compare (in C/ObjC; this is on by default in C++) 
 -Wformat 
 -Wint-in-bool-context 
 -Wimplicit (C and Objective-C only) 
 -Wimplicit-int (C and Objective-C only)
 -Wimplicit-function-declaration (C and Objective-C only) 
 -Winit-self (only for C++) 
 -Wlogical-not-parentheses 
 -Wmain (only for C/ObjC and unless -ffreestanding) 
 -Wmaybe-uninitialized 
 -Wmemset-elt-size   
 -Wmemset-transposed-args 
 -Wmisleading-indentation (only for C/C++) 
 -Wmissing-attributes 
 -Wmissing-braces (only for C/ObjC) 
 -Wmultistatement-macros 
 -Wnarrowing (only for C++) 
 -Wnonnull 
 -Wnonnull-compare      
 -Wopenmp-simd 
 -Wparentheses 
 -Wpointer-sign 
 -Wreorder 
 -Wrestrict 
 -Wreturn-type 
 -Wsequence-point 
 -Wsign-compare (only in C++) 
 -Wsizeof-pointer-div 
 -Wsizeof-pointer-memaccess 
 -Wstrict-aliasing 
 -Wstrict-overflow=1  
 -Wstringop-truncation 
 -Wswitch 
 -Wtautological-compare 
 -Wtrigraphs 
 -Wuninitialized 
 -Wunknown-pragmas 
 -Wunused-function 
 -Wunused-label 
 -Wunused-value 
 -Wunused-variable 
 -Wvolatile-register-var

 -Wclobbered 
 -Wcast-function-type 
 -Wempty-body 
 -Wignored-qualifiers 
 -Wimplicit-fallthrough=3 
 -Wmissing-field-initializers 
 -Wmissing-parameter-type (C only) 
 -Wold-style-declaration (C only) 
 -Woverride-init     
 -Wsign-compare (C only) 
 -Wtype-limits 
 -Wuninitialized 
 -Wshift-negative-value (in C++03 and in C99 and newer) 
 -Wunused-parameter (only with -Wunused or -Wall) 
 -Wunused-but-set-parameter (only with -Wunused or -Wall)