Printf问题。 [英] Printf question.
问题描述
我今天想知道一些事情。以下代码：
unsigned char a = 200;
char b = 200;
printf（"％d％ d"，a，b）;
给出：
200，-56
怎么会？我没告诉printf第一个参数是未签名的
并且它自己检测到了它。 varargs似乎不太可能。
怎么可能？
谢谢，
Hi,
I was wondering something today. The following code :
unsigned char a = 200;
char b = 200;
printf( "%d %d", a, b );
gives :
200, -56
How comes? I didn''t tell printf that the first argument was unsigned
and it detected it on its own. It doesn''t seem possible with varargs.
How is it possible?
Thanks,
推荐答案
praeiji< sp ******* @ gmail.com>写道：
praeiji <sp*******@gmail.com> wrote:
unsigned char a = 200;
char b = 200;
printf（"％d％d"，a，b）;
给出：
200，-56
怎么来的？我没告诉printf第一个参数是未签名的
并且它自己检测到了它。 varargs似乎没有可能。
怎么可能？
unsigned char a = 200;
char b = 200;
printf( "%d %d", a, b );
gives :
200, -56
How comes? I didn''t tell printf that the first argument was unsigned
and it detected it on its own. It doesn''t seem possible with varargs.
How is it possible?
两个参数在传递给printf（）之前都被提升为int br />
_Ico
-
：wq
^ X ^ Cy ^ K ^ X ^ C ^ C ^ C ^ C
Both arguments get promoted to int before they are passed to printf()
_Ico
--
:wq
^X^Cy^K^X^C^C^C^C
谢谢，
但是他们为什么要对int进行类型转换呢？它是否来自gcc，当它看到
"％d"和printf函数？
Thanks,
But why are they typecasted to int? Does it come from gcc when it sees
"%d" and the printf function?
praeiji写道：
praeiji wrote:
<我今天想知道什么。以下代码：
unsigned char a = 200;
char b = 200;
printf（"％d％d"，a，b）;
给出：
200，-56
怎么来的？我没告诉printf第一个参数是未签名的
并且它自己检测到了它。 varargs似乎不太可能。
怎么可能？
谢谢，
Hi,
I was wondering something today. The following code :
unsigned char a = 200;
char b = 200;
printf( "%d %d", a, b );
gives :
200, -56
How comes? I didn''t tell printf that the first argument was unsigned
and it detected it on its own. It doesn''t seem possible with varargs.
How is it possible?
Thanks,
转换参数转换默认Pre -
Specifier Type Value Base cision
％d int x（int）x 10 1
这意味着％d格式为int 。如果你给它char和unsigned char它
将它们转换为int。
Conversion Argument Converted Default Pre-
Specifier Type Value Base cision
%d int x (int)x 10 1
That means %d formats int. If you give it char and unsigned char it
will convert them to int.
这篇关于Printf问题。的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
