No sscanf Expected Type Warnings When Used Through A Template

[Thomas Thorne]

Good Morning, 

I have come across something that I feel a shortcoming in the warnings
that gcc issues when compiling some C++ code.  Calling it a bug seems a
bit harsh so I thought I would ask this mailing list of their opinion
before raising an issue.  When I use a template to perform some sscanf
work on a string I loose some of the -Wformat warnings about the
expected argument types.  

Here is a set of C++ code that demonstrates the warnings occurring for
sscanf and not happening for the template.  

-----
#include <stdio.h>

template<class...Ts>
bool message_scanner(const char *message, const char *format, Ts
const&...ts)
{
  size_t num_scanned(sscanf(message,format,ts...));
  bool got_them_all(num_scanned == sizeof...(ts));
  return got_them_all;
}

int main () 
{
  bool correct(false);
  short int anInt(0);
  char aChar('c');
  float aFloat(0.0);

  char* message = "EXAMPLE001:01,02";

  // No warnings are given about expected argument types for the
template
  if(message_scanner(message,"<EXAMPLE%x:%x,%i",&anInt,&aChar,&aFloat))
  {
    correct = true;
  }

  // Warnings are given about expected argument types 
  if(2==sscanf(message,"<EXAMPLE%x:%x,%i",&anInt,&aChar,&aFloat))
  {
    correct = true;
  }

  return correct?0:1;
}

-----

Perhaps I am doing something wrong with the way I am handling this
template.  There is probably a macro equivalent or some other way this
could be handled and retain the warnings but I found it interesting they
were lost here.  I assume that is because templates are handled not by
code substitution but at a later stage so there is never a sscanf
function produced for GCC to check.  

When I compile the above with GCC 4.8.4 I get:
$ gcc sscanf_template_warnings_example.cpp
sscanf_template_warnings_example.cpp:3:15: warning: variadic templates
only available with -std=c++11 or -std=gnu++11 [enabled by default]
 template<class...Ts>
               ^
sscanf_template_warnings_example.cpp:4:75: warning: variadic templates
only available with -std=c++11 or -std=gnu++11 [enabled by default]
 bool message_scanner(const char *message, const char *format, Ts
const&...ts)

^
sscanf_template_warnings_example.cpp: In function ‘bool
message_scanner(const char*, const char*, const Ts& ...)’:
sscanf_template_warnings_example.cpp:7:42: warning: variadic templates
only available with -std=c++11 or -std=gnu++11 [enabled by default]
   bool got_them_all(num_scanned == sizeof...(ts));
                                          ^
sscanf_template_warnings_example.cpp: In function ‘int main()’:
sscanf_template_warnings_example.cpp:18:19: warning: deprecated
conversion from string constant to ‘char*’ [-Wwrite-strings]
   char* message = "EXAMPLE001:01,02";
                   ^
sscanf_template_warnings_example.cpp:27:64: warning: format ‘%x’ expects
argument of type ‘unsigned int*’, but argument 3 has type ‘short
int*’ [-Wformat=]
   if(2==sscanf(message,"<EXAMPLE%x:%x,%i",&anInt,&aChar,&aFloat))
                                                                ^
sscanf_template_warnings_example.cpp:27:64: warning: format ‘%x’ expects
argument of type ‘unsigned int*’, but argument 4 has type
‘char*’ [-Wformat=]
sscanf_template_warnings_example.cpp:27:64: warning: format ‘%i’ expects
argument of type ‘int*’, but argument 5 has type ‘float*’ [-Wformat=]


Note that all the warnings are about line 27, the sscanf line but none
are given about the templated version.  


Do people think this is worthy of me raising a bug?  
Is there a better way I could be handling the sscanf work without making
it so that the developer has to correct tally up the number of items
that should be scanned?  There are a couple of dozen items in some of
the strings I must parse, so the odds of a mistake now or in a future
update are high.  

-- 
Thomas Thorne <tafthorne@googlemail.com>

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