为什么是“Hello World” const char *？ [英] Why is "Hello World" const char* ?
问题描述
你好，
为什么所有的C / C ++人都写道：
const char * str =" Hello" ;;
或
const char [] str =" Hello";
为什么这不是更优雅的方式：
const unsigned char * str =" Hello" ;; （或[]）
??
我的Reasson：你见过ASCII码：-50？如果你使用''char''
而不是''unsigned char''，扩展的ASCII Set
（> 127）将用负数表示。
谢谢！
汉斯
Hans写道05/02/05：为什么所有的C / C ++人都写道：
没有C / C ++这样的东西。有C，有C ++。他们
是不同的语言（例如在C中，''A''是int和C ++，''A''是
char）
const char * str =" Hello";
const char [] str =" Hello" ;;
两者都是正确的，但有不同的语义（指针与数组）。
为什么这不是更优雅的方式：
const unsigned char * str =" Hello" ;; （或[]）
??
有时会出现类型错误。
我的Reasson：你见过ASCII码：-50？如果使用''char''代替
''unsigned char''，则扩展的ASCII集（> 127）
将由负数表示。
''char''，'unsigned''char和''signed char''是三种不同的
类型。字符串的类型（'char''以0结尾的数组）是
....''char''。期间。
请注意，根据实施情况，可以签署char汽车或
未签名。使用< limits.h>中定义的常量得到当前范围
值。
-
Emmanuel
C-FAQ ： http://www.eskimo.com/~scs /C-faq/faq.html
C库： http://www.dinkumware.com/refxc.html
C是一个锋利的工具
>为什么这不是更优雅的方式：
const unsigned char * str =" Hello" ;; （或[]）
??
这里的char是签名还是未签名并不重要。如果你做了一些
数学的东西，如char /
char a;
a = 127;
a ++;
if（a> 0）....
是否签名可能是个问题。但是当你只想处理
文本时，它没有任何区别。
Hans写道：
为什么这不是更优雅的方式：
const unsigned char * str =" Hello" ;; （或[]）
int main（）
{
const unsigned char * str =" Hello" ;;
}
错误信息全部说明：
C：\ c> g ++ temp.cpp -o temp.exe
temp.cpp：在函数`int main（）''中：
temp.cpp：3：错误：从`const char *''无效转换为`const unsigned
char *''
temp.cpp：4：2：警告：文件末尾没有换行符
C：\c> ; cl temp.cpp
Microsoft（R）32位C / C ++优化编译器版本14.00.41013（适用于80x86）
temp.cpp
temp.cpp（3）：错误C2440：''初始化''：无法转换''const
char [6]''
到''const unsigned char *''
指向的类型不相关;转换需要
reinterpret_cast，C-
样式演员或函数式演员
C：\ c>
-
Ioannis Vranos
http://www23.brinkster.com/noicys
Hello,
Why all C/C++ guys write:
const char* str = "Hello";
or
const char[] str = "Hello";
Why is this not a more elegant way:
const unsigned char* str = "Hello"; (or [])
??
My Reasson: have you ever seen ASCII-Code: -50? The extended ASCII Set
(>127) would be represented by a negative number if you use ''char''
instead of ''unsigned char''.
Thanks!
Hans
Hans wrote on 05/02/05 :Why all C/C++ guys write:
There is no such thing like ''C/C++''. There is C and there is C++. They
are different languages (e.g. in C, ''A'' is an int and in C++, ''A'' is a
char)
const char* str = "Hello";
or
const char[] str = "Hello";
Both are correct, but have different semantic (pointer vs array).
Why is this not a more elegant way:
const unsigned char* str = "Hello"; (or [])
??
Would be a type error sometimes.
My Reasson: have you ever seen ASCII-Code: -50? The extended ASCII Set (>127)
would be represented by a negative number if you use ''char'' instead of
''unsigned char''.
A ''char'', an ''unsigned'' char and a ''signed char'' are three different
types. The type for a string (an array of ''char'' terminated by a 0) is
.... ''char''. Period.
Note that depending on the implementation, a ''char'' car be signed or
unsigned. Use constants defined in <limits.h> to get the current range
values.
--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html
"C is a sharp tool"
> Why is this not a more elegant way:
const unsigned char* str = "Hello"; (or [])
??
It is not important whether char is signed or unsigned here. If you do some
maths things with char like
char a;
a = 127;
a++;
if(a > 0)....
whether it is signed or not may be a problem. But when you just wanna handle
text, it makes no difference.
Hans wrote:
Why is this not a more elegant way:
const unsigned char* str = "Hello"; (or [])
int main()
{
const unsigned char* str = "Hello";
}
The error messages say it all:
C:\c>g++ temp.cpp -o temp.exe
temp.cpp: In function `int main()'':
temp.cpp:3: error: invalid conversion from `const char*'' to `const unsigned
char*''
temp.cpp:4:2: warning: no newline at end of file
C:\c>cl temp.cpp
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.41013 for 80x86
Copyright (C) Microsoft Corporation. All rights reserved.
temp.cpp
temp.cpp(3) : error C2440: ''initializing'' : cannot convert from ''const
char [6]''
to ''const unsigned char *''
Types pointed to are unrelated; conversion requires
reinterpret_cast, C-
style cast or function-style cast
C:\c>
--
Ioannis Vranos
http://www23.brinkster.com/noicys
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