Splitting a `char[]` in C++ - c++

Question

I have a char[] in YYYYMMDDHHMMSS format.
e.g. 2011052504572
I want to retrieve the year, month, date, hour, minute and second from this char. How do I do that?
NOTE:I cant use any third party dll.
Thanks,
Syd

Answer 1

If you're using the STL then just put the string into a std::string and use the substr method:
std::string dateTime=......;
std::string year=dateTime.substr(0,4);
std::string month=dateTime.substr(4,2);
// etc
// etc

Answer 2

Use string::substr() for this purpose. Example,
string date = "20110524112233";
string year = date.substr(0, 4);
string month = date.substr(4, 2);
string day = date.substr(6, 2);
string hour = date.substr(8, 2);
string minute = date.substr(10, 2);
string second = date.substr(12, 2);

Answer 3

It depends on whether you want to extract the values as text, or convert them to numbers. For getting lots of strings, you can use std::string and substr() as thoroughly illustrated in other answers.
If you want to get numbers that you can then calculate with, then one approach is:
int year, month, day, hour, minute, second;
if (sscanf(input, "%.4d%.2d%.2d%.2d%.2d%.2d",
&year, &month, &day, &hour, &minute, &second) == 6)
{
// all 6 conversions worked... can use the values...
int second_in_day = hour * 3600 + minute * 60 + second;
...
}
Another approach is to use strptime() - if your system has it. It parses a string into a broken-down-time structure:
struct tm tm;
strptime(input, "%Y%m%d%H%M%S", &tm);
// parsed values are in tm.tm_year, tm.tm_mon, tm.tm_mday,
// tm.tm_hour, tm.tm_min, tm.tm_sec
// further, tm_wday has day of week, tm_yday has day in year
// i.e. it actually understands the date, not just chopping up numbers/text
Note: sscanf() and strncpy() are C functions callable from C++, and they're not as safe to use as C++-specific functionality (std::string, std::istringstream) in that small misunderstandings and mistakes in handling the data can lead to not just erroneous results, but program crashes. So, read the manual pages for these things carefully if you use them.

Answer 4

Use strncpy... okay, so if it is not homework, then this is the best way. The others using std::string are wasting resources:
static const char *yyyymmddhhmmss = "20110526101559";
char year[5] = { '\0' };
char month[3] = { '\0' };
char day[3] = { '\0' };
char hour[3] = { '\0' };
char minute[3] = { '\0' };
char second[3] = { '\0' };
strncpy(year, yyyymmddhhmmss, 4);
strncpy(month, &yyyymmddhhmmss[4], 2);
strncpy(day, &yyyymmddhhmmss[6], 2);
strncpy(hour, &yyyymmddhhmmss[8], 2);
strncpy(minute, &yyyymmddhhmmss[10], 2);
strncpy(second, &yyyymmddhhmmss[12], 2);

Answer 5

Since you have the input in the form of a char[] (or char*—for
this use, it comes out to the same thing), the simplest solution is
probably using the two iterator constructors for std::string to creat
a string for each field, e.g.:
std::string year ( date , date + 4 );
std::string month( date + 4, date + 6 );
std::string day ( date + 6, date + 8 );
// ...
If you need the numerical values, boost::lexical_cast can be used,
e.g.:
int extractField( char const* string, int begin, int end )
{
return boost::lexical_cast<int>(
std::string( date + begin, date + end ) );
}
int year = extractField( date, 0, 4 );
int year = extractField( date, 4, 6 );
// ...