How to convert Datetime to Unix timestamp in C++

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    #include <iostream>
    #include <ctime>
    
    int main() {
        // Define the date and time (e.g., 2022-05-15 09:50:45)
        tm dateTime = {};
        dateTime.tm_year = 2022 - 1900;  // Year since 1900
        dateTime.tm_mon = 5 - 1;         // Month (0-based, so May is 4)
        dateTime.tm_mday = 15;           // Day of the month
        dateTime.tm_hour = 9;
        dateTime.tm_min = 50;
        dateTime.tm_sec = 45;
    
        // Convert the tm structure to a Unix timestamp
        time_t unixTimestamp = mktime(&dateTime);
    
        // Print the Unix timestamp
        std::cout << "Unix Timestamp: " << unixTimestamp << std::endl;
    
        return 0;
    }

Output:

Unix Timestamp: 1652608245

Example only. There may be multiple ways to perform this operation.

Code Explanation

In this C++ example, the tm structure is initialized to represent the date 2022-05-15 08:10:45. The fields of the tm structure are filled in manually: tm_year is the number of years since 1900, and tm_mon is 0-based, so they are adjusted accordingly.
The mktime() function then converts the tm structure into a Unix timestamp, representing the number of seconds since the Unix epoch (January 1, 1970). The resulting Unix timestamp is 1652602245, which corresponds to the specified date and time.

Convert Unix timestamp to Date in C++

Other useful C++ date functions

Function	Description	Example
`time()`	Returns the current Unix timestamp (seconds since January 1, 1970).	`time_t now = time(nullptr);` returns 1693227296 (current timestamp)
`localtime()`	Converts a Unix timestamp to a `tm` structure representing local time.	`localtime(&now)` returns a `tm` structure for local time
`gmtime()`	Converts a Unix timestamp to a `tm` structure representing UTC (Coordinated Universal Time).	`gmtime(&now)` returns a `tm` structure for UTC time
`mktime()`	Converts a `tm` structure representing local time into a Unix timestamp.	`time_t timestamp = mktime(&tm_struct);` converts `tm` to a timestamp
`strftime()`	Formats a `tm` structure into a string according to a format string.	`strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", &tm_struct);` returns a formatted string
`difftime()`	Returns the difference in seconds between two Unix timestamps.	`double diff = difftime(time1, time2);` returns the time difference in seconds
`asctime()`	Converts a `tm` structure to a string representing the local date and time.	`asctime(&tm_struct)` returns a string, e.g., Wed Aug 28 12:34:56 2024
`ctime()`	Converts a Unix timestamp to a string representing the local date and time.	`ctime(&now)` returns a string, e.g., Wed Aug 28 12:34:56 2024
`std::chrono::system_clock::now()`	Returns the current time point as a `std::chrono::time_point` object.	`auto now = std::chrono::system_clock::now();` returns the current time
`std::chrono::duration_cast()`	Converts one duration type to another (e.g., seconds to milliseconds).	`std::chrono::duration_cast(duration);` converts duration

Current Unix Timestamp SECONDS SINCE JAN 01 1970

Current UTC Time

2025-08-20