Время с эпохи -1

Я пытаюсь узнать количество секунд, прошедших с начала эпохи. Код:

long parseTime(string time) {

cout << "Time entered = " << time << endl;

long timeSinceEpoch;

//takes in time in string format - date + time and returns seconds from epoch.
/* Steps:
* 1. Remove trailing and leading spaces.
* 2. Check format of date.
* 3. Convert to epoch.
*/

//remove trailing and leading spaces.
/*
unsigned int leading = 0, trailing = 0;
string whitespace = " \t";

leading = time.find_first_not_of(whitespace);
trailing = time.find_last_not_of(whitespace);

string newTime = time.substr(leading, (trailing - leading + 1));
cout << "Old time = " << time << " new time = " << newTime << endl;
*/
string newTime = time;

struct tm t;

if(newTime.find("/") != string::npos) {
//format of date is mm/dd/yyyy. followed by clock in hh:mm (24 hour clock).
cout << "Time format contains slashes." << endl;
if(strptime(newTime.c_str(), "%m/%e/%Y %H:%M", &t) == NULL) {
cout << "Error. Check string for formatting." << endl;
}
} else if(newTime.find("-") != string::npos) {
//format of date is yyyy-mm-dd hh:mm:ss (hh in 24 hour clock format).
if(strptime(newTime.c_str(), "%Y-%m-%e %H:%M:%S", &t) == NULL) {
cout << "Error. Check string for formatting of new date." << endl;
}
}

if(t.tm_isdst) {
t.tm_isdst = 0;
}

timeSinceEpoch = mktime(&t);
cout << "Time since epoch = " << timeSinceEpoch << endl;

return timeSinceEpoch;
}

Теперь, когда строка, содержащая дату и время, передается функции:
3/26/2013 3:17
Это приводит ко времени, начиная с эпохи = -1. Вот вывод отладчика:

Breakpoint 2, parseTime (time=...) at informationExtractor.cpp:44
44        cout << "Time entered = " << time << endl;
(gdb) n
Time entered = 3/26/2013 3:17
66        string newTime = time;
(gdb)
70        if(newTime.find("/") != string::npos) {
(gdb) p newTime
$3 = {static npos = <optimized out>,
_M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>},
_M_p = 0x8004ab0c "3/26/2013 3:17"}}
(gdb) n
72          cout << "Time format contains slashes." << endl;
(gdb)
Time format contains slashes.
73          if(strptime(newTime.c_str(), "%m/%e/%Y %H:%M", &t) == NULL) {
(gdb)
83        if(t.tm_isdst) {
(gdb) p newTime.c_str()@strlen(newTime.c_str())
Only values in memory can be extended with '@'.
(gdb) n
84          t.tm_isdst = 0;
(gdb) p newTime
$4 = {static npos = <optimized out>,
_M_dataplus = {<std::allocator<char>> = {<__gnu_cxx::new_allocator<char>> = {<No data fields>}, <No data fields>},
_M_p = 0x8004ab0c "3/26/2013 3:17"}}
(gdb) n
87        timeSinceEpoch = mktime(&t);
(gdb) p t
$5 = {tm_sec = 1628993312, tm_min = 17, tm_hour = 3, tm_mday = 26, tm_mon = 2, tm_year = 113, tm_wday = 2, tm_yday = 84,
tm_isdst = 0}
(gdb) n
88        cout << "Time since epoch = " << timeSinceEpoch << endl;
(gdb)
Time since epoch = -1
90        return timeSinceEpoch;
(gdb)

Если вы заметили, tm_sec в t 1628993312 в то время как timesinceEpoch это -1. tm_sec также хорошо в пределах диапазона для long который является типом данных timesinceEpoch, Любые идеи о том, почему и как решить эту проблему, приветствуются.