[PATCH] Win32: Don't discards const qualifiers for WriteFile

Maxim Dounin mdounin at mdounin.ru
Tue Nov 27 13:27:06 UTC 2018


On Tue, Nov 27, 2018 at 02:07:45PM +0900, Kentaro Hayashi wrote:

> Hi,
> It seems that there is a mismatch between ngx_write_fd and WriteFile
> prototype.
> I've attached a patch for it.
> # HG changeset patch
> # User hayashi at clear-code.com
> # Date 1543294459 -32400
> #      Tue Nov 27 13:54:19 2018 +0900
> # Branch use-const-void-pointer
> # Node ID 04809b6012bd8a744e3beded6fc385cdb3f788ee
> # Parent  a7ff19afbb14795fef14f599a304d0ad21052b70
> Win32: Don't discards const qualifiers for WriteFile
> The 2nd argument of ngx_write_fd() is declared as
> void pointer instead of const void pointer.
> It means that void pointer is passed to WriteFile which accepts
> LPCVOID pointer, instead of LPVOID. Thus const qualifier isn't respected.
> ref.
> https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-writefile
> It causes a compile warning.

Could you please elaborate a bit more about the compile warning?  
Which compiler you use, how the warning looks like?

The const qualifier is only important when it's removed from a 
variable - that is, when you pass something declared as "const" 
into a function with non-const argument.  That is, when you pass a 
constant variable into a function which does not promise to handle 
it as a constant variable.  The opposite is perfectly fine, so you 
can safely pass a non-constant variable into a function which 
promises not to change the variable.  From this point of view 
there are no problems in ngx_write_fd(), it simply passes a 
non-constant string to a function which promises not to change 
this string.


Maxim Dounin

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