How to avoid Switch Case & sscanf Function - c++

Question

I am working on C++. I am writing code for date format. Using with, we can get default date format from anyother date format. So I have found 240 date formats for this task. So M want to use switch case and sscanf function. Every case have sscanf function to separate day,month, year. So I need 240 cases and 240 sscanf function. Is there any method to avoid lot of swtich and sscanf? If you have any ideas, please let me know guys.
case 0:
sscanf(tsdate.c_str(),"%2d/%2d/%4d",&day,&month,&year);
break;
case 1:
sscanf(tsdate.c_str(),"%2d-%2d-%4d",&month,&day,&year);
break;
case 2:
sscanf(tsdate.c_str(),"%2d %2d %4d",&day,&month,&year);
break;
case 3:
sscanf(tsdate.c_str(),"%2d/%2d/%2d",&day,&month,&year);
coryear(year);
break;
case 4:
sscanf(tsdate.c_str(),"%2d/%2d/%2d",&year,&month,&day);
coryear(year);
break;
Like above, I want to put 240 cases and 240 sscanf. Please let me know how to avoid a lot of cases.

Answer 1

you can't avoid the switch cases but you can create multiple function to avoid sscanf:
void scanDayFirst(string format)
{
sscanf(tsdate.c_str(),format,&day,&month,&year);
break;
}
void scanMonthFirst(string format)
{
sscanf(tsdate.c_str(),format,&month,&day,&year);
break;
}
and so on.....
the result will be like this:
case 0:
scanDayFirst("%2d/%2d/%4d");
case 1:
scanDayFirst("%2d-%2d-%4d");
case 2:
scanDayFirst("%2d %2d %4d");
case 3:
scanDayFirst("%2d.%2d.%4d");

Answer 2

enum { ITEM_YEAR, ITEM_MONTH, ITEM_DAY, NUM_ITEMS };
struct date_format { char const *fmt; int items[NUM_ITEMS]; };
struct date_format const formats[] =
{ { "%2d/%2d/%4d", { ITEM_DAY, ITEM_MONTH, ITEM_YEAR } }
, { "%2d-%2d-%4d", { ITEM_MONTH, ITEM_DAY, ITEM_YEAR } }
/* etc. */
};
int parts[NUM_ITEMS]; /* Instead of year,month,day */
sscanf(tsdate.c_str(), formats[x].fmt,
&parts[formats[x].items[0]],
&parts[formats[x].items[1]],
&parts[formats[x].items[2]]);
You can extend this to have ITEM_NONE if you want to skip an item, or add extra items, and so on.
NB. If this is C++ then consider using stream input instead of sscanf.

Answer 3

Instead of enumerating all cases consider instead using a custom language for the format specification:
Date x = parseDate(user_input, "dd-mm-yyyy");
it will make the function shorter, easier to document and easier to use also improving the readability of the code that uses it. The idea is using codes like
yyyy ............. 4-digits year
yy ............... 2-digits year with automatic century computation
mm ............... 2-digits month
m ................ 1 or 2 digits month
dd ............... 2-digits day
d ................ 1 or 2 digits day
anything else .... mandatory character
A simple implementation could be
Date parseDate(const std::string& input, const std::string& format) {
const char *src = input.c_str();
const char *fmt = format.c_str();
int year=-1, month=-1, day=-1;
while (*fmt) {
if (!*src) throw invalid_date(input, format);
if (strncmp(fmt, "yyyy", 4) == 0) {
fmt += 4;
year = getInt(src, 4);
} else if (strncmp(fmt, "yy", 2) == 0) {
fmt += 2;
year = guess_century(getInt(src, 2));
} else if (strncmp(fmt, "mm", 2) == 0) {
fmt += 2;
month = getInt(src, 2);
} else if (fmt[0] == 'm') {
fmt += 1;
month = getInt(src, -1);
} else if (strncmp(fmt, "dd", 2) == 0) {
fmt += 2;
day = getInt(src, 2);
} else if (fmt[0] == 'd') {
fmt += 1;
day = getInt(src, -1);
} else {
if (src[0] != fmt[0]) throw invalid_date(input, format);
src++; fmt++;
}
}
if (*src || year == -1 || month == -1 || day == -1)
throw invalid_date(input, format);
return Date(year, month, day);
}
NOTE: untested