英文:
When I use ctypes.c_int() it returns a different number?
问题
当我使用下面的代码时，它返回一个不同的数字。
numb = 5000000000
n = ctypes.c_int(numb)
它转换的数字是：705032703
更新
现在它不会报错，并执行了操作。然而，它返回的数字仍然不同。它应该返回我输入的数字，但它没有返回。
main.py
numb = 5000000000
n = ctypes.c_int64(numb)
x = hello_world(n)
print(x)
我将Golang代码转换为C代码
main.go
package main
import "C"
func helloWorld(x int64) int64 {
s := int64(1)
for i := int64(1); i < x; i++ {
s = i
}
return s
}
英文:
> When I use the code below, it returns a different number.
>
>
> numb = 5000000000
> n = ctypes.c_int(numb)
>
> the number it converts : 705032703
UPDATE
now it doesn't give error. and performed the operation. However, the number it returns is still different. It should return the number I entered. but it does not return.
main.py
numb = 5000000000
n = ctypes.c_int64(numb)
x = hello_world(n)
print(x)
golang code that I converted to c code
main.go
package main
import "C"
func helloWorld(x int64) int64 {
s := int64(1)
for i := int64(1); i < x; i++ {
s = i
}
return s
}
答案1
得分: 2
5,000,000,000对于32位整数来说太大了。你可以看到下面的示例中它被截断为32位：
>>> n=5000000000
>>> hex(n)
'0x12a05f200' # 33位
>>> import ctypes
>>> hex(ctypes.c_int(n).value)
'0x2a05f200' # 去掉了第33位
你也可以通过与32位掩码进行按位与操作来看到相同的结果：
>>> n & 0xffffffff
705032704
英文:
5,000,000,000 is too large for a 32-bit integer. You can see below it just truncates to 32 bits:
>>> n=5000000000
>>> hex(n)
'0x12a05f200' # 33 bits
>>> import ctypes
>>> hex(ctypes.c_int(n).value)
'0x2a05f200' # dropped the 33rd bit
You can see the same thing by ANDing with a 32-bit mask:
>>> n & 0xffffffff
705032704
答案2
得分: 1
ctypes暴露了与C兼容的类型，其中ctypes.c_int()是有符号int类型的一种暴露，根据平台的不同（甚至可能更窄或更宽），它可以是32位或64位。
在您的实例中，您的c_int是32位类型，32位有符号整数可以保存范围[-2147483648, 2147483647]，或者有4294967296个可能的值。
因此，它无法直接保存您的5000000000（50亿），并且溢出处理方式是由实现定义的。
如果您想保存大数，建议使用固定宽度类型，如c_int64，这样您就可以确切地知道自己在处理什么，因为c_int和c_long具有一些大小保证，但在其他方面是实现/平台特定的。
英文:
ctypes exposes the C-compatible types, with ctypes.c_int() being an exposure of the signed int type, which could be 32-bit or 64-bit depending on the platform (or possibly even narrower or wider).
In your instance, your c_int is a 32-bit type, and a 32-bit signed int can hold the range [-2147483648, 2147483647], or 4294967296 possible values.
So it can't hold your 5000000000 (5 billion) as-is, and it's implementation-defined how overflow is handled.
If you want to hold large numbers, it's recommended to used fixed-width types like c_int64 so you know exactly what you're dealing with, as c_int and c_long have some size guarantees but are otherwise implementation/platform specific.
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