Thread: printf() issue on Windows

I'm having trouble getting the value of a unsigned long long to print to stdout... here's the program:

Code:

// Some code omitted

int main()
{
	unsigned long long d, t;
	unsigned int f = 0;

	d = 5;
	t = 9;

	printf("d = %lld, t = %lld.\n", d, t);
	printf("Is d prime? %d\nIs t prime? %d\n", isPrime(d), isPrime(t));

	for(t = 2; f < 1000; t++)
	{
		if(isPrime(t)) { printf("%lld\n", t); f++; }
	}
	
	return 0;
}

It compiles fine, with no errors (GCC, 'gcc -Wall -o primetest.exe primetest.c') but the first few lines of output are:

Code:

d = 5, t = 0.
Is d prime? 1
Is t prime? 0
2
3
5
7
...

It should, by my reasoning, say 'd = 5, t = 9', yet it doesn't.
To complicate things, this only occurs under (you guessed it) Windows. (Windows 98) It compiles fine under Windows, Linux and OS/2, but gives the expected output '...t = 9' only on Linux and OS/2. Windows gives t = 0.

So I tried to simplify it with:

Code:

#include <stdio.h>

int main()
{
	unsigned long long a = 1, b = 2, c = 3, d = 4;

	printf("Output:");

	printf("\na = %lld", a);
	printf("\na = %lld, b = %lld", a, b);
	printf("\na = %lld, b = %lld, c = %lld", a, b, c);
	printf("\na = %lld, b = %lld, c = %lld, d = %lld", a, b, c, d);

	printf("\n");
	return 0;
}

Which gives:

Code:

Output:
a = 1
a = 1, b = 0
a = 1, b = 0, c = 2
a = 1, b = 0, c = 2, d = 0

Again, only on Windows! OS/2 and Linux once again agree with the output of:

Code:

...
a = 1, b = 2, c = 3, d = 4

I'm clueless as to what's going on... thanks in advance for any help.

Originally Posted by n7yap

-std='c99' maybe?

As written, that gives:
cc1.exe: error: unrecognized command line option "-std='99'"
If I remove the single quotes, it accepts it, but the problem is not solved using:
gcc -std=c99 -Wall -o primetest.exe primetest.c
I've no idea what -std=c99 does, and I haven't been able to find any documentation on it.

I'm using gcc (Mingw) 3.4.2 btw.

MinGW uses the Microsoft C Run-time library, and that library does not support C99. It requires %I64 instead of %ll for printf. The GCC compiler supports C99, with the command-line switch, so it supports the long long data type. The equivalent data type in VC is _int64.

So that's why it wouldn't work. What about long doubles?

http://msdn.microsoft.com/library/de...ong_double.asp

In Win32 programming, however, the long double data type maps to the double, 64-bit precision data type.

That was my problem . . . thanks.

Originally Posted by n7yap

MinGW uses the Microsoft C Run-time library, and that library does not support C99. It requires %I64 instead of %ll for printf. The GCC compiler supports C99, with the command-line switch, so it supports the long long data type. The equivalent data type in VC is _int64.

That solved it! The odd output makes much more sense now, and the %I64 corrects the problem. (Do they do this just to make porting apps harder?)

The program compiles & runs fine without the -std=c99 (the documentation said the default dialect uses some features of c99... long long must be one of them.). Still, good to know.

Thanks to everyone who helped.