Ticket #6815: main.2.cpp

#include "templ_literal.h"
#include <cstddef>
#include <stdio.h>

template< class >
struct FormatSupportedType;

#define SUPPORTED_TYPE(C, T) \
template<> struct FormatSupportedType< T > \
{ \
        constexpr static bool supports(char c) \
        { return ( c == C ); } \
}

SUPPORTED_TYPE('c', char);
SUPPORTED_TYPE('d', int);

template< std::size_t N >
constexpr bool checkFormatHelper( const char (&format)[N], std::size_t current )
{
        return
                current >= N ?
                        true
                : format[current] != '%' ?
                        checkFormatHelper( format, current + 1 )
                : format[current + 1] == '%' ?
                        checkFormatHelper( format, current + 2 )
                :
                        false;
}

template< std::size_t N, class T, class... Ts >
constexpr bool checkFormatHelper( const char (&format)[N], std::size_t current, const T& arg, const Ts & ... args )
{
        return
                current >= N ?
                        false
                : format[current] != '%' ?
                        checkFormatHelper( format, current + 1, arg, args... )
                : (format[current] == '%' && format[current + 1] == '%') ?
                        checkFormatHelper( format, current + 2, arg, args... )
                : FormatSupportedType< T >::supports(format[current + 1]) &&
                        checkFormatHelper( format, current + 2, args... );
}

template< std::size_t N, class... Ts >
constexpr bool checkFormat( const char (&format)[N], const Ts & ... args )
{
        return checkFormatHelper( format, 0, args... );
}

#define safe_printf_1(FORMAT, ...) \
        static_assert(checkFormat( FORMAT, __VA_ARGS__ ), "Format is incorrect"); \
        printf(FORMAT, __VA_ARGS__)

template< char... FORMAT, class... ARGS >
int safe_printf_2(TemplateLiteral<FORMAT...>, ARGS... args)
{
        constexpr char format[] = {FORMAT... , '\0'};
        static_assert( checkFormat(format, args... ), "Format is incorrect");
        return printf( format, args... );
}

int main()
{
        safe_printf_1("%c %d", 'x', 257);
        safe_printf_2(TEMPLATE_LITERAL("%c %d"), 'x', 257);
}