char与signed char, unsigned char的区别
2013-10-14 22:57
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转自:http://blog.csdn.net/superleexpert/article/details/7640803
今天有一个困扰的问题,就是char与signed char, unsigned char这三者的区别,本着不睡觉的牺牲精神,总结一下学来的东西。
1.ANSI C 提供了3种字符类型,分别是char、signed char、unsigned char。而不是像short、int一样只有两种(int默认就是unsigned int).
2.三者都占1个字节
3.signed char取值范围是 -128 到 127(有符号位) unsigned char 取值范围是 0 到 255
4.内存中一串二进制,它的含义,就是这个类型来说明的。
5.所谓signed char 和 unsigned char 其实是相对“运算”而说的,已经脱离了我们字面含义“字符”,表示的范围有限。
1.char的定义
C标准中对char是 Impementation Defined,就是未明确定义
(1)那它由什么定义?坦白说,具体的编译器明确定义,一般都是用signed char或unsigned char来实现char的,也就是说不同的编译器对char是什么定义不一样
(2)为什么要这样定义?因为这三种类型的对象在存储介质中的表现形式是一样的(都是一个占8bit的01串,只是解析的时候不同)
(3)到底是signed char还是unsigned char?这得看编译器:VC编译器、x86上的GCC都把char定义为signed char,而arm-linux-gcc却把char定义为 unsigned char
2.char的使用
char的不同使用给了它不同的字面上的含义
(1)当字符用
原始的ASCII标准里,定义的字符码值是只有0~127,所以怎么定义的char都刚好好装得下,于是普通意义上我们对它的理解就是它表示一个字符,也就是让表示一个ASCII码(这也是C语言基础中对它的解释)
(2)当单字节整数
从本质上来说,字符(‘a’, ‘b’, ‘c’等)本质上也是一个整数,只是字符代表的值是0~127,我们可以用char表示一个不太大的整数
说明:我们现在默认为VC的这一套 char 定义为 signed char
首先在内存中,char 与unsigned char没有什么不同,都是一个字节,8个bit,普通的赋值,读写文件和网络字节流都没什么区别,反正就是一个字节,不管最高位是什么,最终的读取结果都一样,只是你怎么理解最高位而已。
好吧,我们认为现在char的最高位为符号位,因此char能表示-128~127, unsigned char没有符号位,因此能表示0~255。
但是屏幕上面的显示可能不一样。
?Download cppkey_down.txt
输出
?Download cppkey_down.txt
所以,在编程中也要非常注意由于unsigned 带来的一些问题
一、开始
今天有一个困扰的问题,就是char与signed char, unsigned char这三者的区别,本着不睡觉的牺牲精神,总结一下学来的东西。
二、三者之间
1.ANSI C 提供了3种字符类型,分别是char、signed char、unsigned char。而不是像short、int一样只有两种(int默认就是unsigned int).2.三者都占1个字节
3.signed char取值范围是 -128 到 127(有符号位) unsigned char 取值范围是 0 到 255
4.内存中一串二进制,它的含义,就是这个类型来说明的。
5.所谓signed char 和 unsigned char 其实是相对“运算”而说的,已经脱离了我们字面含义“字符”,表示的范围有限。
三、char
1.char的定义C标准中对char是 Impementation Defined,就是未明确定义
(1)那它由什么定义?坦白说,具体的编译器明确定义,一般都是用signed char或unsigned char来实现char的,也就是说不同的编译器对char是什么定义不一样
(2)为什么要这样定义?因为这三种类型的对象在存储介质中的表现形式是一样的(都是一个占8bit的01串,只是解析的时候不同)
(3)到底是signed char还是unsigned char?这得看编译器:VC编译器、x86上的GCC都把char定义为signed char,而arm-linux-gcc却把char定义为 unsigned char
2.char的使用
char的不同使用给了它不同的字面上的含义
(1)当字符用
原始的ASCII标准里,定义的字符码值是只有0~127,所以怎么定义的char都刚好好装得下,于是普通意义上我们对它的理解就是它表示一个字符,也就是让表示一个ASCII码(这也是C语言基础中对它的解释)
(2)当单字节整数
从本质上来说,字符(‘a’, ‘b’, ‘c’等)本质上也是一个整数,只是字符代表的值是0~127,我们可以用char表示一个不太大的整数
四、关于高位扩展
说明:我们现在默认为VC的这一套 char 定义为 signed char首先在内存中,char 与unsigned char没有什么不同,都是一个字节,8个bit,普通的赋值,读写文件和网络字节流都没什么区别,反正就是一个字节,不管最高位是什么,最终的读取结果都一样,只是你怎么理解最高位而已。
好吧,我们认为现在char的最高位为符号位,因此char能表示-128~127, unsigned char没有符号位,因此能表示0~255。
但是屏幕上面的显示可能不一样。
五、举例实践:
?Download cppkey_down.txt1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | [cpp] view plaincopyprint? <span style="padding:0px; margin:0px; color:rgb(102,102,102)">// ----------------------------------</span> <span style="padding:0px; margin:0px; color:rgb(102,102,102)">// 说明:char测试</span> <span style="padding:0px; margin:0px; color:rgb(102,102,102)">// 环境:VS2008</span> <span style="padding:0px; margin:0px; color:rgb(102,102,102)">// 时间:2011.8.31</span> <span style="padding:0px; margin:0px; color:rgb(102,102,102)">//-----------------------------------</span> <span style="padding:0px; margin:0px; color:rgb(51,153,0)">#include "stdafx.h"</span> <span style="padding:0px; margin:0px; color:rgb(51,153,0)">#include<limits></span> <span style="padding:0px; margin:0px; color:rgb(51,153,0)">#include<iostream></span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">using</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">namespace</span> std<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">void</span> f<span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">unsigned</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span> v<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span> <span style="padding:0px; margin:0px; color:rgb(0,128,0)">{</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span> c <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> v<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">unsigned</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span> uc <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> v<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">unsigned</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span> a <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> c, b <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> uc<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span> i <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> c, j <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> uc<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">printf</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"----------------<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">printf</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"%%c: %c, %c<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span>, c, uc<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">printf</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"%%X: %X, %X<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span>, c, uc<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">printf</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"%%u: %u, %u<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span>, a, b<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">printf</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"%%d: %d, %d<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span>, i, j<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,128,0)">}</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span> main<span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span> argc, <span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span><span style="padding:0px; margin:0px; color:rgb(0,0,64)">*</span> argv<span style="padding:0px; margin:0px; color:rgb(0,128,0)">[</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">]</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span> <span style="padding:0px; margin:0px; color:rgb(0,128,0)">{</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">cout</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"min char is : "</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span>numeric_limits<span style="padding:0px; margin:0px; color:rgb(0,0,128)"><</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)">></span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">::</span><span style="padding:0px; margin:0px; color:rgb(0,119,136)">max</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"max char is : "</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span>numeric_limits<span style="padding:0px; margin:0px; color:rgb(0,0,128)"><</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)">></span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">::</span><span style="padding:0px; margin:0px; color:rgb(0,119,136)">min</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"char is signed ? "</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> numeric_limits<span style="padding:0px; margin:0px; color:rgb(0,0,128)"><</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)">></span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">::</span><span style="padding:0px; margin:0px; color:rgb(0,119,136)">is_signed</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span>endl<span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">char</span> c <span style="padding:0px; margin:0px; color:rgb(0,0,128)">=</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">127</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> c<span style="padding:0px; margin:0px; color:rgb(0,0,64)">++</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">cout</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">static_cast</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)"><</span><span style="padding:0px; margin:0px; color:rgb(0,0,255)">int</span><span style="padding:0px; margin:0px; color:rgb(0,0,128)">></span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span>c<span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span> <span style="padding:0px; margin:0px; color:rgb(0,0,128)"><<</span> <span style="padding:0px; margin:0px; color:rgb(255,0,0)">"<span style="padding:0px; margin:0px; color:rgb(0,0,153)"><strong>\n</strong></span>"</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> f<span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(32,128,128)">0x80</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> f<span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(32,128,128)">0x7F</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">system</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">(</span><span style="padding:0px; margin:0px; color:rgb(255,0,0)">"pause"</span><span style="padding:0px; margin:0px; color:rgb(0,128,0)">)</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,0,255)">return</span> <span style="padding:0px; margin:0px; color:rgb(0,0,221)">0</span><span style="padding:0px; margin:0px; color:rgb(0,128,128)">;</span> <span style="padding:0px; margin:0px; color:rgb(0,128,0)">}</span> |
?Download cppkey_down.txt
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | [text] view plaincopyprint? min char is : 127 max char is : -128 char is signed ? 1 -128 ---------------- %c: €, € %X: FFFFFF80, 80 %u: 4294967168, 128 %d: -128, 128 ---------------- %c: , %X: 7F, 7F %u: 127, 127 %d: 127, 127 |
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