为什么我不能直接将__int64变量设置为-2500000000？

Question

此程序是在WindowsXP计算机上的VC ++ 6.0中写入的。

如果我尝试将__int64变量直接设置为-25000000，它被截断到32位值，并且拍摄了两个的补充。

__int64 testval;
testval = -2500000000;

. 在此目的中，TETVAL等于1794967293（1101010 1111 1101 0000 0111 00000000二进制）。

当我将变量设置为2500000000然后乘以负数时，它有效：

__int64 testval;
testval = 2500000000;
testval *= -1;

.

变量testval等于-2500000000（1001 0101 0000 0010 1111 1001 0000 0000二进制）。

任何想法？ 谢谢。

Answer 1

Get a newer compiler. VC6 standard compliance is VERY poor.

In VC6, try a suffix of i64, as in

__int64 toobig = -2500000000i64;

Found the documentation!

Answer 2

The compiler is treating the constant 2500000000 as a 32-bit number. You need to explicitly tell it to treat it as a long int by appending an LL to the end of the constant. So, try instead:

testval = -2500000000LL;

Update: Since your compiler doesn't support this, and you are stuck with VC6, try instead breaking it into a value that results from the product of two 32 bit numbers as in:

testval = -250000;
testval *= 10000;

Answer 3

The correct syntax is -2500000000LL. If it doesn't work, get a newer compiler.