Here is one simple and primitive way.
void TestDayString()
{
std::string IC( "190508143749" );
char yearStr[ 4 ] = { 0 };
char monthStr[ 4 ] = { 0 };
char dayStr[ 4 ] = { 0 };
strncpy( yearStr, & IC[0], 2 );
strncpy( monthStr, & IC[2], 2 );
strncpy( dayStr, & IC[4], 2 );
int year = atoi( yearStr );
int month = atoi( monthStr );
int day = atoi( dayStr );
printf( "year, month, days are %02d %02d %02d\n", year, month, day );
}
as an added bonus, I tried it and it works.