printf a 64-bit number

[Richard Cavell]

GCC 3.3, XCode:


#include <iostream>
#include <stdint.h>

int main (int argc, char * const argv[])
{
uint64_t a=10123123123LL;
printf("%d\n", a);
std::cout << a;
std::cout << "\n";
return 0;
}

The printf statement gives me 2 (which is the upper 32 bits of a). The
cout gives me the correct result. Is this expected behaviour? Surely
64 bit integers are de rigeur now.

I'm generally trying to use C and not C++ for portability and speed.

 

[void]

GCC 3.3, XCode:


#include <iostream>
#include <stdint.h>

int main (int argc, char * const argv[])
{
uint64_t a=10123123123LL;
printf("%d\n", a);

printf("%lld\n", a);

Best
Darek

 

[Rolf Magnus]

GCC 3.3, XCode:


#include <iostream>
#include <stdint.h>

int main (int argc, char * const argv[])
{
uint64_t a=10123123123LL;
printf("%d\n", a);
std::cout << a;
std::cout << "\n";
return 0;
}

The printf statement gives me 2 (which is the upper 32 bits of a). The
cout gives me the correct result. Is this expected behaviour?

Yes. You specified %d to printf, which means that you promised to pass an
int. But since you didn't actually pass an int, the result will be wrong.

Surely 64 bit integers are de rigeur now.

I'm generally trying to use C and not C++ for portability and speed.

What makes you believe printf is more portable and faster than cout? Do you
have any evidence that proves this?

 

[msalters]

GCC 3.3, XCode:


#include <iostream>
#include <stdint.h>

int main (int argc, char * const argv[])
{
uint64_t a=10123123123LL;
printf("%d\n", a);
std::cout << a;
std::cout << "\n";
return 0;
}

The printf statement gives me 2 (which is the upper 32 bits of a). The
cout gives me the correct result. Is this expected behaviour? Surely
64 bit integers are de rigeur now.

I'm generally trying to use C and not C++ for portability and speed.

Well, uint64_t isn't really portable. But I guess this shows:
with C it's easy to be wrong everywhere. You're probably very fast
in producing the wrong answer, but C++ is even faster:
in main() { } also produces the wrong output. It's also smaller.
The moral: being right is more important than petty concerns.

HTH,
Michiel Salters