C语言 如何在C中显示unsigned long long的最大值？
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How to display the maximum value of a unsigned long long in C?
提问by Lazer
What am I doing wrong here?
我在这里做错了什么？
$ cat size.c
#include<stdio.h>
#include<math.h>
int main() {
printf ("sizeof unsigned int = %d bytes.\n", sizeof(unsigned int));
printf ("sizeof unsigned long long = %d bytes.\n", sizeof(unsigned long long));
printf ("max unsigned int = %d\n", (int)(pow(2, 32) - 1));
printf ("max unsigned long long = %lld\n", (unsigned long long)(pow(2, 64) - 1));
}
$ gcc size.c -o size
$ ./size
sizeof unsigned int = 4 bytes.
sizeof unsigned long long = 8 bytes.
max unsigned int = 2147483647
max unsigned long long = -1
$
I am expecting 18446744073709551615as output instead of a -1at the last line.
我期望18446744073709551615作为输出而不是-1最后一行。
Okay, I completely missed that I was getting the wrong value for 232- 1, which should have been 4294967295, not 2147483647. Things make more sense now.
好吧，我完全没有注意到我得到了错误的 2 32- 1值，它应该是 4294967295，而不是 2147483647。现在事情变得更有意义了。
回答by Jens Gustedt
Just don't suppose that it has a certain value use ULLONG_MAX
只是不要假设它有一定的价值用途 ULLONG_MAX
回答by sepp2k
Use %llu, not %lld. dis for signed integers, so printfdisplays it as a signed long long.
使用%llu，不是%lld。d用于有符号整数，因此将其printf显示为有符号 long long。
回答by slezica
Edit: changed ~0 to (type) -1 as per Christoph's suggestion. See the comments below.
编辑：根据克里斯托夫的建议，将 ~0 更改为 (type) -1。请参阅下面的评论。
You can get the maximum value of an unsigned type doing the following:
您可以通过执行以下操作获得无符号类型的最大值：
unsigned long long x = (unsigned long long) -1;
Easier, right? =). Second, you are telling printf()to interpret the given variable as a long long decimal, which is signed. Try this instead:
更容易，对吧？=)。其次，您告诉printf()将给定的变量解释为带符号的长长十进制数。试试这个：
unsigned long long x = (unsigned long long) -1;
printf("%llu", x);
%llumeans "long long unsigned".
%llu意思是“long long unsigned”。
回答by Kiril Kirov
unsigned long long ulTestMax = -1;
printf ("max unsigned long long = %llu\n", ulTestMax );
this works in C++, should work here, too.
这适用于 C++，也应该适用于这里。
回答by cyber_raj
Whoever done -1 to Kiril Kirov post pls take a look here:
谁对基里尔·基洛夫 (Kiril Kirov) 发表了 -1 评论，请看这里：
Is it safe to use -1 to set all bits to true?Dingo post
In Kiril post only slight modification required regarding sign extension:
在 Kiril 帖子中，仅需要对符号扩展进行轻微修改：
unsigned long long ulTestMax = -1LLu;
-1 is antipattern, it'll do the job if u dont want to go with the solution provided by lmits.h
-1 是反模式，如果你不想使用 lmits.h 提供的解决方案，它会完成这项工作
