On Tue, Jul 5, 2022 at 12:21 AM Yair Lenga via Gcc <gcc@gcc.gnu.org> wrote: > > Hi, > > Wanted to get some feedback on an idea that I have - trying to address the > age long issue with type check on VA list function - like 'scanf' and > friends. In my specific case, I'm trying to build code that will parse a > list of values from SELECT statement into list of C variables. The type of > the values is known (by inspecting the result set meta-data). My ideal > solution will be to implement something like: > > int result_set_read(struct result_set *p_result_set, ...); > > Which can be called with > > int int_var ; float float_var ; char c[20] ; > result_set_read(rs1, &int_var, &float_var, c) ; > > The tricky part is to verify argument type - make sure . One possible path > I thought was - why not leverage the ability to describe scanf like > functions ( > result_set_read(rs1, const char *format, ...) __attribute((format (scanf, > 2, 3)) ; > > And then the above call will be > result_set-read(rs1, "%d %f %s", &int_var, &float_var, c) ; > > With the added benefit that GCC will flag as error, if there is mismatch > between the variable and the type. My function parses the scanf format to > decide on conversions (just the basic formatting '%f', '%d', '%*s', ...). > So far big improvement, and the only missing item is the ability to enforce > check on string sizes - to support better checks against buffer overflow > (side note: wish there was ability to force inclusion of the max string > size, similar to the sscanf_s). > > My question: does anyone know how much effort it will be to add a new GCC > built-in (or extension), that will automatically generate a descriptive > format string, consistent with scanf formatting, avoiding the need to > manually enter the formatting string. This can be thought of as "poor man > introspection". Simple macro can then be used to generate it > > #define RESULT_SET_READ(rs, ...) result_set_read(rs, > __builtin_format(__VA_ARGS__), __VA_ARGS__) > > Practically, making the function "safe" (with respect to buffer overflow, > type conversions) for most use cases. > > Any feedback, pointers, ... to how to implement will be appreciated
This is all recorded as https://gcc.gnu.org/PR47781 . You could do a plugin to handle the attribute maybe. Thanks, Andrew Pinski > > Yair
