CODEWITHSUNDEEP
c++unixundefined-behaviorgettimeofday
heyblackduck
heyblackduck

Reputation: 117

Undefined behavior using gettimeofday

#include <iostream>
#include <sys/time.h>

static long elapsedTime(struct timeval &then)
{
    struct timeval when;
    gettimeofday(&when, NULL);
    long result = (when.tv_sec - then.tv_sec) * 1000;
    result += (when.tv_usec - then.tv_usec) / 1000;
    then = when;
    return (result > 0) ? result : 0;
}

int main()
{
    struct timeval now;
    gettimeofday(&now, NULL);

    long elapsed, everyMinute = 0;
    while (true) {
        elapsed = elapsedTime(now);
        everyMinute += elapsed;

        if (everyMinute % 1000 == 0) 
            std::cout << "After: " << everyMinute << std::endl;
    }
    return 0;
}

I am trying to get this loop to print every minute but gettimeofday gives me unexpected behavior. For example this line std::cout << "Before: " << everyMinute << std::endl; will cause the if to work but without it I just get zeros: here is snippet but it is better to plug into your own compiler.

Upvotes: 1

Views: 875

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