C++ converting string to time_t question

Question

Im trying to convert a string such as "12 August 2011" into time_t or that seconds elapsed, or whatever so I can use it to compare a list of dates.

At the moment, I have tried the following but the output seems to equal false! Also, the seconds elapsed seem to keep changing?

Is this correct?

#include <iostream>
#include <string>
#include <cstdlib>
#include <cstring>
#include <time.h>
#include <stdio.h>

using namespace std;

int main()
{

    struct tm tmlol, tmloltwo;
    time_t t, u;

    t = mktime(&tmlol);
    u = mktime(&tmloltwo);
    //char test[] = "01/01/2008";string test = "01/01/2008";

    strptime("10 February 2010", "%d %b %Y", &tmlol);
    strptime("10 February 2010", "%d %b %Y", &tmloltwo);

    t = mktime(&tmlol);
    u = mktime(&tmloltwo);

    cout << t << endl;
    cout << u << endl;

    if (u>t)
    {
        cout << "true" << endl;
    }
    else if (u==t)
    {
        cout << "same" << endl;
    }
    else
    {
        cout << "false" << endl;
    }

    cout << (u-t);
}

shinkou · Accepted Answer · 2011-08-18 01:50:27Z

8

You should initialize the structs before use. Try this:

#include <iostream> 
#include <string>
#include <cstdlib>
#include <cstring>
#include <time.h>
#include <stdio.h>          

using namespace std;

int main()
{
    struct tm tmlol, tmloltwo;
    time_t t, u;

    // initialize declared structs
    memset(&tmlol, 0, sizeof(struct tm));
    memset(&tmloltwo, 0, sizeof(struct tm));

    strptime("10 February 2010", "%d %b %Y", &tmlol);         
    strptime("10 February 2010", "%d %b %Y", &tmloltwo);

    t = mktime(&tmlol);
    u = mktime(&tmloltwo);

    cout << t << endl;
    cout << u << endl;

    if (u>t)
    {
        cout << "true" << endl;
    }
    else if (u==t)
    {
        cout << "same" << endl;
    }
    else
    {
        cout << "false" << endl;
    }

    cout << (u-t) << endl;

    return 0;
}

answered Aug 18, 2011 at 1:50

shinkou

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2 Comments

Keith Thompson Over a year ago

Simpler: struct tm tmlol = { 0 }; struct tm tmloltwo = { 0 };. (gcc may warn about missing initializers; feel free to ignore it.)

Keith Thompson Over a year ago

@ildjarn: Interesting. That's illegal in C; I didn't know C++ allowed it.

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