timeval not returning expecting results

Question

I have some code shown below:

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

typedef struct{
     struct timeval timestamp;
}teststruct;

class TestClass {
     public:
       TestClass();
       void dosomething(int, int);
};

TestClass::TestClass(){
}

void
TestClass::dosomething(int num, int numb) {
}

int main(void){
     TestClass *testclass = new TestClass();
     teststruct test;
     gettimeofday(&test.timestamp, NULL);
     printf("%llu \n", test.timestamp.tv_sec);
     testclass->dosomething(1,1);
     printf("%llu \n", test.timestamp.tv_sec);
}

The output of this code is:

13825459612132795564 dosomething 5598307500

but I have no idea why the first number is messed up. Also the class call is completely necessary in order for the numbers to be different from one another.

Answer 1

I get warning: format ‘%llu’ expects type ‘long long unsigned int’, but argument 2 has type ‘__time_t’. Should be a hint. Up your compiler's warning level to something sensible.

It works when you use the proper input type. You were invoking UB otherwise, reading memory that wasn't yours to read; bugs like this can yield funny results that behave differently based on factors that you wouldn't normally expect to make a difference, as the contents of your memory change.

Answer 2

Seems to work if you change the %llu to %lu.

http://codepad.org/YGubabLR