Loading... 今天在一份源码中看到了 `gcc -W -Wall ...`，自己平时没有用过，于是查了下`gcc`手册。 ## 查询说明 使用`mac gcc`查找三个选项的说明： ### `-w` ```bash -w Inhibit all warning messages. ``` 从上面可以看出来`-w`是代表关闭编译时的所有警告，也就是不显示任何`Warning`。 ### `-Wall` ```bash -Wall This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options. -Wall turns on the following warning flags: -Waddress -Warray-bounds=1 (only with -O2) -Wbool-compare -Wbool-operation -Wc++11-compat -Wc++14-compat -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-braces (only for C/ObjC) -Wnarrowing (only for C++) -Wnonnull -Wnonnull-compare -Wopenmp-simd -Wparentheses -Wpointer-sign -Wreorder -Wreturn-type -Wsequence-point -Wsign-compare (only in C++) -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtautological-compare -Wtrigraphs -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value -Wunused-variable -Wvolatile-register-var Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually. ``` 从中可以看出， -Wall选项会显示所有的警告。 ### `-W` 在 `man gcc`中并没有找到有关 `-W` 的选项，从Google搜索中得知`-W`选项类似于`-Wall`，会显示警告，但只会显示编译器认为会出现错误的警告。 ## 举个例子 代码： ```c #include <stdio.h> void main(){ int i = 3; float ii = i; printf("Hello, World!"); return 0; } ``` 直接编译： ```bash rainshaw@Ubuntu-Linux:~$ gcc main.c -o a.out main.c: In function ‘main’: main.c:6:12: warning: ‘return’ with a value, in function returning void return 0; ^ main.c:2:6: note: declared here void main(){ ^~~~ rainshaw@Ubuntu-Linux:~$ ``` 出现了一个警告。 使用 `-w`参数，我们现在知道肯定没有任何警告（x ```bash rainshaw@Ubuntu-Linux:~$ gcc -w -o a.out main.c rainshaw@Ubuntu-Linux:~$ ``` 使用 `-Wall`参数： ```bash rainshaw@Ubuntu-Linux:~$ gcc -Wall -o a.out main.c main.c:2:6: warning: return type of ‘main’ is not ‘int’ [-Wmain] void main(){ ^~~~ main.c: In function ‘main’: main.c:6:12: warning: ‘return’ with a value, in function returning void return 0; ^ main.c:2:6: note: declared here void main(){ ^~~~ main.c:4:9: warning: unused variable ‘ii’ [-Wunused-variable] int ii = i; ^~ rainshaw@Ubuntu-Linux:~$ ``` 显示了所有的警告，包括了变量`ii`未使用的警告。 使用`-W`参数： ```bash rainshaw@Ubuntu-Linux:~$ gcc -W -o a.out main.c main.c: In function ‘main’: main.c:6:12: warning: ‘return’ with a value, in function returning void return 0; ^ main.c:2:6: note: declared here void main(){ ^~~~ rainshaw@Ubuntu-Linux:~$ ``` 只显示了返回值不匹配的`Warning`。 使用`-W -Wall`参数： ```bash rainshaw@Ubuntu-Linux:~$ gcc -W -Wall -o a.out main.c main.c:2:6: warning: return type of ‘main’ is not ‘int’ [-Wmain] void main(){ ^~~~ main.c: In function ‘main’: main.c:6:12: warning: ‘return’ with a value, in function returning void return 0; ^ main.c:2:6: note: declared here void main(){ ^~~~ main.c:4:9: warning: unused variable ‘ii’ [-Wunused-variable] int ii = i; ^~ rainshaw@Ubuntu-Linux:~$ ``` 比单独使用`-W`参数多了一些警告。 ## 后记 在Google搜索过程中，看到这样一种说法： > 编译时不使用`-W -Wall`选项是`stupid`的 所以以后还是都带上为好。 最后修改：2020 年 10 月 11 日 05 : 27 PM © 允许规范转载 赞赏 如果觉得我的文章对你有用，请随意赞赏 ×Close 赞赏作者 扫一扫支付 支付宝支付 微信支付
