输出字符'A'/'a'的解析

输出字符'A'/'a'的代码段：

?1???? //?Test1:?Directly?insert?0x0A?and?0x41?to?ostream
?2

????cout?<<?0x0A;????//?print?type?int?10
?3

????cout?<<?'?';
?5

????cout?<<?0x41;????//?print?type?int?65,?which?is?decimal?number?of?'A'.
?7

????cout?<<?'?';
?8

????//?Test2:?Directly?insert?'\x41'?to?ostream
10

????cout?<<?'\x41';????//?'\x41'?is?transformed?char,?which?means?type?char?'A'.
11

?????????????????????? //?So,?it?prints?type char 'A'? on screen.
12

????cout?<<?'?';
13

????//?Test3:?First?assign?0x41?to?char?variable,?then?output?it.
15

????char?char_out?=?0x41;????//?char_out?is?equal?'A'?which?is?type?int?65.
16

????cout?<<?char_out;????????//?it?prints?type?char?'A'?on?screen.
17

????cout?<<?'?';
19

????//?Test4:?First?cast?0x0A?to?char,?then?output?it.
20

????cout?<<?static_cast<char>(0x41); // it prints type char 'A' on screen.
21

????
22

????cout?<<?'?';

23

????//?Test5:?Directly?insert?hexdecimal?type?number?of?'A'

24?????cout?<<?std::hex /*<<?std::showbase*/?<<?0x41;?//?it?prints?string?literal?"41"?
25

????cout?<<?'?'?<<?std::hex?<<?0x0A;?//?it?prints?type?char 'a' on screen.
26

????int?int_out?=?'0x41';
27

????cout?<<?int_out;?//?it?prints?type?int?8342**
28

????cout?<<?endl;

?? 0x41是字符'A'的16进制表示方式，它的10进制数是65，\x41是字符'A'的转义字符。而0x0A跟字符'A'没有丝毫关系，顶多就是0x0A借用了字符'A'而已。故如果想在屏幕上输出字符'A'可将其转义字符直接插入输出流中，或者将0x41转化为字符类型，然后插入，不得使用0x41直接插入，因为0x41本身是int类型的10进制数65。同时也不可以将'0x41'直接插入输出流，因为'0x41'是int类型的数。
?? 可以尝试使用控制符std::hex来插入字符'a'到输出流。

posted on 2007-01-15 10:59 仄洛阅读(24) 评论(0) 编辑收藏收藏至365Key 所属分类: C++ Performance

输出字符'A'/'a'的解析

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