Timestamp Functions

What is a Unix timestamp?

A Unix timestamp is the number of seconds that have elapsed since the Unix epoch: 1970-01-01 00:00:00 UTC. It is an integer value (commonly stored in C as time_t) that represents an absolute point in time independent of any time-zone. Note that typical Unix timestamps count whole seconds (not milliseconds) and POSIX time does not account for leap seconds.

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Task

Implement two functions for working with timestamps in the chat server.

Function 1: get_current_timestamp

• Returns the current Unix timestamp (seconds since epoch)

Function Signature

// Returns the current time as a Unix timestamp
time_t get_current_timestamp(void);

Function 2: format_timestamp

• Takes a Unix timestamp and formats it as a string in the format YYYY-MM-DD HH:MM
• Writes the formatted string to the provided buffer

Function Signature

// Format a timestamp as "YYYY-MM-DD HH:MM" and write to buffer 
void format_timestamp(time_t timestamp, char* buffer);

Timestamp Format

The timestamp format should be:

YYYY-MM-DD HH:MM

Where:

• YYYY is the four-digit year, like 2024
• MM is the two-digit month (01-12), like 10 for October
• DD is the two-digit day (01-31), like 06
• HH is the two-digit hour in 24-hour format (00-23), like 09 for 9am or 14 for 2pm
• MM is the two-digit minute (00-59), like 01 or 45

All values should be zero-padded. For example:

• 2024-10-06 09:01 (correct)
• 2024-10-6 9:1 (incorrect - missing zero padding)

Note

• For get_current_timestamp, use the time() system call from <time.h>
• For format_timestamp, use localtime() and strftime() from <time.h>
• The strftime() function with format string "%Y-%m-%d %H:%M" produces the exact format needed
• The buffer for format_timestamp will always be large enough (at least 17 bytes)
• Include <time.h> for the time functions

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Example

Unix Timestamp	Formatted Output
1728219660	2024-10-06 09:01
1728219720	2024-10-06 09:02
1728219840	2024-10-06 09:04
0	1970-01-01 00:00
1609459200	2021-01-01 00:00

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Code

#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
time_t get_current_timestamp(void)
{
    return time(NULL);
}
 
void format_timestamp(time_t timestamp, char *buffer)
{
    struct tm* timeinfo = localtime(&timestamp);
    strftime(buffer, 32, "%Y-%m-%d %H:%M", timeinfo);
}
 
int main(int argc, char **argv)
{
    if (argc < 2)
    {
        printf("Usage: %s <timestamp>\n", argv[0]);
        return 1;
    }
 
    // Test format_timestamp with provided timestamp
    time_t t = (time_t)atoll(argv[1]);
    char buffer[32];
    format_timestamp(t, buffer);
    printf("%s\n", buffer);
 
    // Optionally test get_current_timestamp
    // time_t current = get_current_timestamp();
    // printf("Current timestamp: %ld\n", current);
 
    return 0;
}