C Date and Time

C Date and Time

In C programming, working with C Date and Time is done using functions defined in the <time.h> library.

This library allows you to:

Get the current date and time
Format date/time
Measure execution time
Convert between time formats

📌 Common Data Type Used: `time_t`

time_t stores calendar time in seconds since January 1, 1970 (Unix Epoch).

1️⃣ Get Current Date and Time

Output (example):

2️⃣ Using `localtime()` to Break Down Time

You can extract year, month, day, time components using struct tm.

#include <stdio.h>
#include <time.h>

int main() {
time_t now = time(NULL);
struct tm *local = localtime(&now);

printf("Year: %d\n", local->tm_year + 1900);
printf("Month: %d\n", local->tm_mon + 1);
printf("Day: %d\n", local->tm_mday);
printf("Time: %02d:%02d:%02d\n", local->tm_hour, local->tm_min, local->tm_sec);

return 0;
}

#include <stdio.h>

#include <time.h>

int main() {

time_t now = time(NULL);

struct tm *local = localtime(&now);

printf("Year: %d\n", local->tm_year + 1900);

printf("Month: %d\n", local->tm_mon + 1);

printf("Day: %d\n", local->tm_mday);

printf("Time: %02d:%02d:%02d\n", local->tm_hour, local->tm_min, local->tm_sec);

return 0;

}

3️⃣ Formatting Time Using `strftime()`

#include <stdio.h>
#include <time.h>

int main() {
time_t now = time(NULL);
struct tm *local = localtime(&now);

char buffer[40];
strftime(buffer, sizeof(buffer), "%d-%m-%Y %H:%M:%S", local);

printf("Formatted Time: %s\n", buffer);
return 0;
}

#include <stdio.h>

#include <time.h>

int main() {

time_t now = time(NULL);

struct tm *local = localtime(&now);

char buffer[40];

strftime(buffer, sizeof(buffer), "%d-%m-%Y %H:%M:%S", local);

printf("Formatted Time: %s\n", buffer);

return 0;

}

Output:

4️⃣ Calculating Time Differences

You can measure how long something takes using difftime().

#include <stdio.h>
#include <time.h>

int main() {
time_t start, end;

time(&start);
printf("Processing...\n");

for(long i=0; i<500000000; i++); // some heavy task

time(&end);

printf("Time taken: %.2f seconds\n", difftime(end, start));
return 0;
}

#include <stdio.h>

#include <time.h>

int main() {

time_t start, end;

time(&start);

printf("Processing...\n");

for(long i=0; i<500000000; i++); // some heavy task

time(&end);

printf("Time taken: %.2f seconds\n", difftime(end, start));

return 0;

}

5️⃣ Converting `struct tm` Back to `time_t`

#include <stdio.h>
#include <time.h>

int main() {
struct tm date = {0};
date.tm_year = 2025 - 1900;
date.tm_mon = 11; // December (0-based)
date.tm_mday = 25;

time_t t = mktime(&date);

printf("Unix timestamp: %ld\n", t);
return 0;
}

#include <stdio.h>

#include <time.h>

int main() {

struct tm date = {0};

date.tm_year = 2025 - 1900;

date.tm_mon = 11; // December (0-based)

date.tm_mday = 25;

time_t t = mktime(&date);

printf("Unix timestamp: %ld\n", t);

return 0;

}

📌 Summary Table

Function	Purpose
`time()`	Returns current time in seconds
`ctime()`	Converts time to readable string
`localtime()`	Converts time_t to structured time
`strftime()`	Formats date/time into a custom string
`difftime()`	Calculates time difference
`mktime()`	Converts structured time back to time_t

C Date and Time

C Date and Time

📌 Common Data Type Used: time_t

1️⃣ Get Current Date and Time

Output (example):

2️⃣ Using localtime() to Break Down Time

3️⃣ Formatting Time Using strftime()

Output:

4️⃣ Calculating Time Differences

5️⃣ Converting struct tm Back to time_t

📌 Summary Table

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📌 Common Data Type Used: `time_t`

2️⃣ Using `localtime()` to Break Down Time

3️⃣ Formatting Time Using `strftime()`

5️⃣ Converting `struct tm` Back to `time_t`