是否可以将long long returne值分配给int64_t而不会在64位计算机上失去精度? [英] Is it possible to assign long long returne value to int64_t without losing the precision in a 64-bit Machine?
问题描述
我已经实现了以下代码:
I have implemented below code :
#include<stdio.h>
#include<string.h>
#include<ctype.h>
#include<cstdlib>
#include<sys/types.h>
main()
{
int64_t i64value1 = 0;
int64_t i64value2 = 0;
long long llvalue = 0;
const char *s = "10811535359";
i64value1 = atoll(s);
llvalue = atoll(s);
i64value2 = llvalue;
printf("s : [%s]\n",s);
printf("i64value1 : [%d]\n",i64value1);
printf("llvalue : [%lld]\n",llvalue);
printf("i64value2 : [%d]\n",i64value2);
}
上述程序的输出是:
s : [10811535359]
i64value1 : [-2073366529]
llvalue : [10811535359]
i64value2 : [-2073366529]
使用的编译器是:
gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)
操作系统为 x86_64 GNU/Linux 2.6.18-194
因为 long long 是一个带符号的64位整数,并且在所有意图和目的上均与 int64_t 类型相同,因此在逻辑上 int64_t 和 long long 应该是等效的类型.有些地方提到使用 int64_t 代替 long long .但是当我查看 stdint.h 时,它告诉我为什么看到上述行为:
Since long long is a signed 64-bit integer and is, for all intents and purposes, identical to int64_t type, logically int64_t and long long should be equivalent types. And some places mention to use int64_t instead of long long. But when I look at stdint.h, it tells me why I see the above behavior:
# if __WORDSIZE == 64
typedef long int int64_t;
# else
__extension__
typedef long long int int64_t;
# endif
在64位编译中, int64_t 是 long int ,而不是 long long int .
In a 64-bit compile, int64_t is long int, not a long long int.
我的问题是,是否有一种解决方法/解决方案,可以将长整型长返回值分配给int64_t,而不会损失64位计算机的精度?
My Question is, Is there a workaround/solution to assign long long returned value to int64_t without losing the precision in 64 bit Machine?
预先感谢
推荐答案
损失不是在转换中发生的,而是在印刷中发生的:
The loss does not happen in the conversions but in the printing:
printf("i64value1 : [%d]\n",i64value1);
像 int
一样访问 int64_t
参数.这是不确定的行为,但是通常低32位是符号扩展的.
The int64_t
argument is accessed as if it were an int
. This is undefined behaviour, but usually the low 32 bits are sign extended.
正确的编译器警告(例如gcc -Wformat
)应该对此有所抱怨.
Proper compiler warnings (such as gcc -Wformat
) should complain about this.
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