How to Determine the Earlier Time Between Two String Time Values in C ?

Conversion of String Time to time_t

Converting a string containing time in "hh:mm:ss" format to time_t in C can be achieved in various ways.

One method is to leverage C 11's advanced time and date manipulation capabilities with and libraries. You can utilize the following steps:

• Define a tm struct.
• Utilize an istringstream to read the time string.
• Extract the time components using get_time.
• Construct a time_t value using mktime.

For example:

std::tm tm;
std::istringstream ss("16:35:12");
ss >> std::get_time(&tm, "%H:%M:%S"); // or just %T in this case
std::time_t time = std::mktime(&tm);

Comparing Time Variables for Earliest Value

To compare two strings containing time, you can either compare their corresponding time_t representations or use string comparison techniques.

Using time_t values, you can directly compare them using std::less. For example:

std::string curr_time = "18:35:21";
std::string user_time = "22:45:31";
std::istringstream ss_curr(curr_time);
std::istringstream ss_user(user_time);
std::tm tm_curr, tm_user;
ss_curr >> std::get_time(&tm_curr, "%H:%M:%S");
ss_user >> std::get_time(&tm_user, "%H:%M:%S");
std::time_t time_curr = std::mktime(&tm_curr);
std::time_t time_user = std::mktime(&tm_user);

if (time_curr < time_user) {
  std::cout << curr_time << " is earlier than " << user_time << std::endl;
} else {
  std::cout << user_time << " is earlier than " << curr_time << std::endl;
}

Alternatively, string comparison can be used, assuming both times are in the same format:

if (curr_time < user_time) {
  std::cout << curr_time << " is earlier than " << user_time << std::endl;
} else {
  std::cout << user_time << " is earlier than " << curr_time << std::endl;
}

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