Help: using time difftime function

Hi,

I have written a function to check if the age of a person is more than 65. The function works fine for BirthDate 1937 and after. But for dates before 1937, the difftime output overflows, and so, the result is wrong.

I tried to declare long double varables to store the result of difftime function and solve the problem, but it didn't work.

I have attached the code. Thanks for your help.
FE

Not very long so I've posted the code for you, people are understandable reluctent to download code...never know what you'll get hehe.

Code:

---

int Age65(const char * BirthDate) {

    /*  BirthDate format is dd-mmm-yyyy  */

    struct tm  TheDate = {0};
    time_t    Birth;
    char      TempString[5];
    int        rc = 0;
    double    YearInSec = 60*60*24*365.4*65;  /*  65 years old in seconds  */

    memset(TempString, 0x00, sizeof(TempString));

    TempString[0] = BirthDate[0];
    TempString[1] = BirthDate[1];
    TempString[2] = '\0';
    TheDate.tm_mday = atoi(TempString);

    memset(TempString, 0x00, sizeof(TempString));
    TempString[0] = BirthDate[3];
    TempString[1] = BirthDate[4];
    TempString[2] = BirthDate[5];
    TempString[3] = '\0';

    if (strcmp(TempString, "JAN") == 0) TheDate.tm_mon =  0;
    if (strcmp(TempString, "FEB") == 0) TheDate.tm_mon =  1;
    if (strcmp(TempString, "MAR") == 0) TheDate.tm_mon =  2;
    if (strcmp(TempString, "APR") == 0) TheDate.tm_mon =  3;
    if (strcmp(TempString, "MAY") == 0) TheDate.tm_mon =  4;
    if (strcmp(TempString, "JUN") == 0) TheDate.tm_mon =  5;
    if (strcmp(TempString, "JUL") == 0) TheDate.tm_mon =  6;
    if (strcmp(TempString, "AUG") == 0) TheDate.tm_mon =  7;
    if (strcmp(TempString, "SEP") == 0) TheDate.tm_mon =  8;
    if (strcmp(TempString, "OCT") == 0) TheDate.tm_mon =  9;
    if (strcmp(TempString, "NOV") == 0) TheDate.tm_mon = 10;
    if (strcmp(TempString, "DEC") == 0) TheDate.tm_mon = 11;

    memset(TempString, 0x00, sizeof(TempString));
    TempString[0] = BirthDate[ 7];
    TempString[1] = BirthDate[ 8];
    TempString[2] = BirthDate[ 9];
    TempString[3] = BirthDate[10];
    TempString[4] = '\0';

    TheDate.tm_year = atoi(TempString) > 1900 ? atoi(TempString) - 1900 : 0;

    Birth = mktime(&TheDate);

    if (difftime(time(NULL), Birth) >= YearInSec) {
      rc = 1;
    }

    return rc;
};

---

Seems that nobody can find a solution to this problem!!!

OK!

But the problem is not in mktime(). The problem is with difftime(). The program give correct result for date 1937 and after that (for example, 13-NOV-1937). But when the difference between two dates is more than 2147483647 (long int!), the result makes overflow and becomes negative.

When I run the attached program for 13-NOV-1920 , I get the following results:

T2=-1550516400 (You called Birth as T2)
Diff = difftime(time(NULL), Birth);
diff: -1707238770.000000
Div = Diff / (60*60*24*365.4)
Div: -54.076924

I expect Div ~= 82
And, when I use long double for varaibles Diff and Div, I have:

T2=-1550516400
diff: -63746071383186921000000000000000000000000000000000 000000.000000,
Div: 360208603066998260000.000000

And it is worse!!!

The result is

Epoch=Wed Dec 31 19:00:00 1969

Now, what shall I do?

> What does this tell you?
That it's a good idea to check return values even in simple examples? ;) This code crashed on me because localtime() returned NULL.