Comparing 2 dates in c++

Question

I was wondering if there is any relatively easy and short date comparison functions in C++. My dates are of type char*, and have the following format: DD

Answer 1

If this is really a fixed format, you can do it with simple C string comparison

int date_cmp(const char *d1, const char *d2)
{
    int rc;
    // compare years
    rc = strncmp(d1 + 6, d2 + 6, 4);
    if (rc != 0)
        return rc;

    // compare months
    rc = strncmp(d1 + 3, d2 + 3, 2);
    if (rc != 0)
        return rc;

    // compare days
    return strncmp(d1, d2, 2);
}

This works like strncmp. It returns a value less than 0, if d1 is earlier than d2, 0 if both are the same date, and a value greater than 0, if d1 is later than d2.

Another approach would be to convert it with strptime and mktime to time_t and compare these with difftime

struct tm tm;
time_t t1, t2;
strptime(d1, "%d\\%m\\%Y", &tm);
t1 = mktime(&tm);
// do the same with d2
double diff = difftime(t1, t2);