Re: [PATCH 2/2] mingw: avoid const warning

Karsten Blees [off-list ref] writes:

Am 29.05.2014 12:47, schrieb Stepan Kasal:

quoted

Fix const warnings in http-fetch.c and remote-curl.c main() where is
argv declared as const.

The fix should work for all future declarations of main, no matter
whether the second parameter's type is "char**", "const char**", or
"char *[]".

I'm 100% in favor of a solution that doesn't restrict main to non-const char**! Thanks.

quoted

Signed-off-by: Stepan Kasal <redacted>
---
 compat/mingw.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/compat/mingw.h b/compat/mingw.h
index 15f0c9d..8745d19 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h

@@ -369,10 +369,11 @@ extern CRITICAL_SECTION pinfo_cs;
 void mingw_startup();
 #define main(c,v) dummy_decl_mingw_main(); \
 static int mingw_main(c,v); \
-int main(int argc, char **argv) \
+int main(c, char **main_argv_not_used) \
 { \
+	typedef v, **argv_type; \
 	mingw_startup(); \
-	return mingw_main(__argc, __argv); \
+	return mingw_main(__argc, (argv_type)__argv); \
 } \
 static int mingw_main(c,v)
 

I have to admit I had trouble understanding what 'typedef v,
**arv_type;' does (looks invalid at first glance), and why you
would need main_argv_not_used instead of just main(c,v).

So, I'd like to award +10 points for cleverness, but -10 for
obscurity ;-) Probably deserves a comment or an explanation in the
commit message.

Agreed.  The "typedef" one is a cute hack.

I am wondering why the solution is not a more obvious "drop const
that is not ANSI C", though.  I only have a ready-access to N1570
draft but in it I find:

    5.1.2.2.1 Program startup

    The function called at program startup is named main. The
    implementation declares no prototype for this function. It shall
    be defined with a return type of int and with no parameters:

    int main(void) { /* ... */ }

    or with two parameters (referred to here as argc and argv,
    though any names may be used, as they are local to the function
    in which they are declared):

    int main(int argc, char *argv[]) { /* ... */ }

    or equivalent;10) or in some other implementation-defined manner.

    ---
    10) Thus, int can be replaced by a typedef name defined as int,
    or the type of argv can be written as char ** argv, and so on.

A simpler solution that works with all definitions of main() is to
cast to void* (tell the compiler all responsibility is on
us).

Can you cast away the constness that way, though?

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