字符串比较。如何比较字符串与std :: wstring？ WRT strcmp [英] String comparisons. How can you compare string with std::wstring? WRT strcmp

问题描述

我想比较两种格式，我预期会有点兼容，因为他们都是字符串。我试图执行strcmp与一个字符串和std :: wstring，并且我确信C ++的古茹知道，这将只是不编译。是否可以比较这两种类型？

I am trying to compare two formats that I expected would be somewhat compatible, since they are both generally strings. I have tried to perform strcmp with a string and std::wstring, and as I'm sure C++ gurus know, this will simply not compile. Is it possible to compare these two types? Is there an easy conversion here?

推荐答案

您需要转换 char * string - ISO C语言中的multibyte - ISO C语言中的 wchar_t * string - wide character。执行此操作的标准函数称为 mbstowcs （多字节字符串到宽字符串）

You need to convert your char* string - "multibyte" in ISO C parlance - to a wchar_t* string - "wide character" in ISO C parlance. The standard function that does that is called mbstowcs ("Multi-Byte String To Wide Character String")

注意在注释中，这是一个C99函数，因此不是ISO C ++一致，但可能支持C ++实现作为扩展。 MSVC和g ++都支持它。

NOTE: as Steve pointed out in comments, this is a C99 function and thus is not ISO C++ conformant, but may be supported by C++ implementations as an extension. MSVC and g++ both support it.

因此：

const char* input = ...;

std::size_t output_size = std::mbstowcs(NULL, input, 0); // get length
std::vector<wchar_t> output_buffer(output_size);

// output_size is guaranteed to be >0 because of \0 at end
std::mbstowcs(&output_buffer[0], input, output_size);

std::wstring output(&output_buffer[0]);

一旦你有两个 wstring 比较像往常一样。注意，这将使用当前系统语言环境进行转换（即在Windows上这将是当前的ANSI代码页） - 通常这只是你想要的，但偶尔你需要处理一个特定的编码，在这种情况下上述操作不会执行，您需要使用 iconv 。

Once you have two wstrings, just compare as usual. Note that this will use the current system locale for conversion (i.e. on Windows this will be the current "ANSI" codepage) - normally this is just what you want, but occasionally you'll need to deal with a specific encoding, in which case the above won't do, and you'll need to use something like iconv.

所有其他答案似乎都用于直接代码点翻译（即相当于（wchar_t）c 对于字符串中的每个 char c ）。这可能不适用于所有区域设置，但它将工作，如果例如。您的 char 都是ASCII或Latin-1，而您的 wchar_t 是Unicode。如果你确定这是你真正想要的，最快的方法是完全避免转换，并使用 std :: lexicographical_compare ：

All other answers seem to go for direct codepoint translation (i.e. the equivalent of (wchar_t)c for every char c in the string). This may not work for all locales, but it will work if e.g. your char are all ASCII or Latin-1, and your wchar_t are Unicode. If you're sure that's what you really want, the fastest way is actually to avoid conversion altogether, and to use std::lexicographical_compare:

#include <algorithm>

const char* s = ...;
std::wstring ws = ...;

const char* s_end = s + strlen(s);

bool is_ws_less_than_s = std::lexicographical_compare(ws.begin, ws.end(),
                                                      s, s_end());
bool is_s_less_than_ws = std::lexicographical_compare(s, s_end(),
                                                      ws.begin(), ws.end());
bool is_s_equal_to_ws = !is_ws_less_than_s && !is_s_less_than_ws;

如果您特别需要测试是否相等，请使用 std :: equal 和一个长度检查：

If you specifically need to test for equality, use std::equal with a length check:

#include <algorithm>

const char* s = ...;
std::wstring ws = ...;

std::size_t s_len = strlen(s);
bool are_equal =
    ws.length() == s_len &&
    std::equal(ws.begin(), ws.end(), s);

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