C ++字符串

C ++字符串 - 如何为wstring实现这个'IsEmptyOrSpace（string）'方法？(C++ Strings - How can I implement this 'IsEmptyOrSpace(string)' method for wstring's?)

好的，我在StackOverflow上搜索了如何检查字符串是空还是只有空格。 但是，它只适用于ANSI字符串。 如何让它与wstring一起使用？

这是代码：

#include <string> using namespace std; //! Checks if a string is empty or is whitespace. bool IsEmptyOrSpace(const string& str) { string::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (*it >= 0 && *it <= 0x7f && isspace(*(it++))); // One of these conditions will be optimized away by the compiler. // Which one depends on whether the characters are signed or not. return false; }

我的第一个想法是将isspace(*(it++))更改为iswspace(*(it++)) ，但之前的两个条件只适用于ASCII，对吧？ 这是我到目前为止尝试将函数调整为wstring的：

bool IsEmptyOrSpaceW(const wstring& str) { String::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (*it >= 0 && *it <= 0x7f && iswspace(*(it++))); // One of these conditions will be optimized away by the compiler. // Which one depends on whether the characters are signed or not. // Do I need to change "*it >= 0 && *it <= 0x7f" to something else? return false; }

我的方法接近正确吗？ 无论哪种方式，我如何实现此IsEmptyOrSpace()函数的Unicode版本？

编辑：好的，如果你需要知道为什么*it >= 0 && *it <= 0x7f测试就在那里，我不能告诉你，因为我不知道。 我从这个问题的答案得到了函数的代码： C ++检查字符串是空格还是空所以让我从头开始，一般来说，我可以检查一下wstring是EMPTY还是只是空格？

Okay, I searched StackOverflow on how to check if a string is empty or just whitespace. But, it only works with ANSI strings. How can I get it to work with a wstring?

Here is the code:

#include <string> using namespace std; //! Checks if a string is empty or is whitespace. bool IsEmptyOrSpace(const string& str) { string::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (*it >= 0 && *it <= 0x7f && isspace(*(it++))); // One of these conditions will be optimized away by the compiler. // Which one depends on whether the characters are signed or not. return false; }

My first thought was to change isspace(*(it++)) to iswspace(*(it++)), but the two conditions before that will only work with ASCII, right? Here is what I have so far on attempting to adapt the function to wstring's:

bool IsEmptyOrSpaceW(const wstring& str) { String::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (*it >= 0 && *it <= 0x7f && iswspace(*(it++))); // One of these conditions will be optimized away by the compiler. // Which one depends on whether the characters are signed or not. // Do I need to change "*it >= 0 && *it <= 0x7f" to something else? return false; }

Is my approach close to being correct? Either way, how can I implement a Unicode version of this IsEmptyOrSpace() function?

EDIT: Okay, if you need to know why the *it >= 0 && *it <= 0x7f test is there, I cannot tell you, because I do not know. I got the code for the function from the answer to this question: C++ check if string is space or null So let me start from scratch, how, in general, may I check if a wstring is EMPTY or just whitespace?

最满意答案

但之前的两个条件只适用于ASCII，对吧？

那就对了。 它们确保该值符合isspace的前提条件：参数“必须具有unsigned char或EOF的值”。 严格地说，你只需要*it >= 0检查，如果char是无符号的，应该优化掉; 或者，如评论中所述，您可以将值转换为unsigned 。

iswspace没有这样的前提条件，所以只需从宽版本中删除这些检查：

bool IsEmptyOrSpaceW(const wstring& str) { wstring::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (iswspace(*(it++))); return false; }

作为一种风格，没有必要添加像W这样的奇怪的疣来表示参数类型，因为你可以用不同的参数类型重载IsEmptyOrSpace 。

but the two conditions before that will only work with ASCII, right?

That's right. They make sure the value conforms to the precondition of isspace: the argument "must have the value of an unsigned char or EOF". Strictly speaking, you only need the *it >= 0 check, which should be optimised out if char is unsigned; alternatively, as mentioned in the comments, you could convert the value to unsigned.

iswspace has no such precondition, so just remove those checks from the wide version:

bool IsEmptyOrSpaceW(const wstring& str) { wstring::const_iterator it = str.begin(); do { if (it == str.end()) return true; } while (iswspace(*(it++))); return false; }

As a matter of style, there's no need to add a strange wart like W to indicate the parameter type, since you can just overload IsEmptyOrSpace with different parameter types.