如何比较C中的多字节字符 [英] How to compare multibyte characters in C

问题描述

我尝试解析文本并在其中找到一些字符.我使用下面的代码.它适用于 abcdef 等普通字符，但不适用于 öçşğüı.GCC 给出编译警告.我应该怎么做才能使用 öçşğüı?

I try to parse text and find some characters in it. I use the code below. It works with normal characters like abcdef but it does not work with öçşğüı. GCC gives compilation warnings. What should I do to work with öçşğüı?

代码:

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main()
{
    char * text = "öçşğü";
    int i=0;

    text = strdup(text);

    while (text[i])
    {       
        if(text[i] == 'ö')
        {
            printf("ö 
");
        }

        i++;
    }

    return 0;
}

警告:

warning: multi-character character constant [-Wmultichar]
warning: comparison is always false due to limited range of data type [-Wtype-limits]

<小时>

在while循环中打印char的地址时有10个地址

---

There are 10 addresses when I print address of char in while loop

printf("%d : %p 
", i, text[i]);

输出:

0 : 0xffffffc3 
1 : 0xffffffb6 
2 : 0xffffffc3 
3 : 0xffffffa7 
4 : 0xffffffc5 
5 : 0xffffff9f 
6 : 0xffffffc4 
7 : 0xffffff9f 
8 : 0xffffffc3 
9 : 0xffffffbc 

而 strlen 是 10.

但如果我使用 abcde:

0 : 0x61 
1 : 0x62 
2 : 0x63 
3 : 0x64 
4 : 0x65 

而 strlen 是 5.

如果我使用 wchar_t 进行文本输出是

If I use wchar_t for text output is

0 : 0xa7c3b6c3 
1 : 0x9fc49fc5 
2 : 0xbcc3 

strlen 为 10，wcslen 为 3.

and strlen is 10, wcslen is 3.

推荐答案

要遍历字符串中的每个字符，可以使用mblen.您还需要设置正确的语言环境(多字节字符串所代表的编码)，以便mblen能够正确解析多字节字符串.

To go through each of the characters in the string, you can use mblen. You also need to set the correct locale (the encoding represented by the multi byte string), so that mblen can correctly parse the multi byte string.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <locale.h>

int main()
{
    char * text = "öçşğü";
    int i=0, char_len;

    setlocale(LC_CTYPE, "en_US.utf8");

    while ((char_len = mblen(&text[i], MB_CUR_MAX)) > 0)
    {
        /* &text[i] contains multibyte character of length char_len */
        if(memcmp(&text[i], "ö", char_len) == 0)
        {
            printf("ö 
");
        }

        i += char_len;
    }

    return 0;
}

有 2 种类型的字符串表示，使用多字节(8 位字节)或宽字节(大小取决于平台).多字节表示具有可以使用 char * 表示的优点(代码中通常使用 c 字符串)，但缺点是多个字节表示一个字符.宽字符串使用 wchar_t * 表示.wchar_t 具有一个 wchar_t 是一个字符的优点(但是正如@anatolyg 指出的那样，在 wchar_t 无法表示所有可能字符的平台上，这种假设仍然可能出错).

There are 2 types of string representation, using multi-byte (8-bit bytes) or wide byte (size depends on platform). Multi-byte representation has the advantage it can be represented using char * (usual c string as in your code), but has disadvantage that multiple bytes represent a character. Wide string is represented using wchar_t *. wchar_t has the advantage that one wchar_t is one character (However as @anatolyg pointed out, this assumption can still go wrong in platforms where wchar_t is not able to represent all possible characters).

您是否使用十六进制编辑器查看过您的源代码?字符串 "öçşğü" 实际上由内存中的多字节字符串 c3 b6 c3 a7 c5 9f c4 9f c3 bc 表示(UTF-8 编码)，当然是零终止.您看到 5 个字符只是因为您的 UTF-8 感知查看器/浏览器正确呈现了字符串.很容易意识到 strlen(text) 为此返回 10，而上面的代码只循环了 5 次.

Have you looked at your source code using a hex editor? The string "öçşğü" actually is represented by multi byte string c3 b6 c3 a7 c5 9f c4 9f c3 bc in memory (UTF-8 encoding), of course with zero termination. You see 5 characters just because the string is rendered correctly by your UTF-8 aware viewer/browser. It is simple to realize that strlen(text) returns 10 for this, whereas the above code loops only 5 times.

如果您使用宽字节字符串，可以按照@WillBriggs 的说明进行操作.

If you use wide-byte string, it can be done as explained by @WillBriggs.

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