Zeug

#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#undef	sizeof
#define	sizeof( ptr ) \
	( ( __builtin_object_size( ptr, 0 ) == -1 ) ? 0 : __builtin_object_size( ptr, 0 ) )

#if 1
	#undef	strcpy
	#define	strcpy( dst, src ) \
		strncpy( dst, src, sizeof( dst ) - 1 ); \
		dst[ sizeof( dst ) - 1 ] = 0

	#undef	strcat
	#define	strcat( dst, src ) \
		strncat( dst, src, sizeof( dst ) - strlen( dst ) - 1 )

	#undef	sprintf
	#define	sprintf( dst, fmt, args ... ) \
		snprintf( dst, sizeof( dst ), fmt, ## args )

	#undef	vsprintf
	#define	vsprintf( dst, fmt, args ) \
		vsnprintf( dst, sizeof( dst ), fmt, args )
#else
	#undef	strcpy
	#define strcpy()
	#undef	strcat
	#define	strcat()
	#undef	sprintf
	#define	sprintf()
	#undef	vsprintf
	#define	vsprintf()
#endif

char buf[ 20 ], *txt;
void vsprintf_test( char *fmt, ... );

int main( int argc, char *argv[] ) {
	txt = "zu langer test string";

	printf( "sizeof( buf ): %d\n", sizeof( buf ) );
	printf( "sizeof( buf + 1 ): %d\n", sizeof( buf + 1 ) );

	strcpy( buf, "12345678901234567890" );
	printf( "buf = %s\n", buf );

	strcpy( buf, "2. " );
	strcat( buf, txt );
	printf( "buf = %s\n", buf );

	sprintf( buf, "%d. %s", 3, txt );
	printf( "buf = %s\n", buf );

	vsprintf_test( "%d. %s", 4, txt );
	printf( "buf = %s\n", buf );

	return 0;
}

void vsprintf_test( char *fmt, ... ) {
	va_list	args;

	va_start( args, fmt );
	vsprintf( buf, fmt, args );
	va_end( args );
}