C++ 如何从C++中的字符串中去除所有非字母数字字符？
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How to strip all non alphanumeric characters from a string in c++?
提问by Austin Witherspoon
I am writing a piece of software, and It require me to handle data I get from a webpage with libcurl. When I get the data, for some reason it has extra line breaks in it. I need to figure out a way to only allow letters, numbers, and spaces. And remove everything else, including line breaks. Is there any easy way to do this? Thanks.
我正在编写一个软件，它要求我使用 libcurl 处理从网页获取的数据。当我获得数据时，由于某种原因，它有额外的换行符。我需要想办法只允许字母、数字和空格。并删除其他所有内容，包括换行符。有什么简单的方法可以做到这一点吗？谢谢。
回答by James McNellis
Write a function that takes a charand returns trueif you want to remove that character or falseif you want to keep it:
编写一个接受 achar并返回的函数，true如果您想删除该字符或false要保留它：
bool my_predicate(char c);
Then use the std::remove_ifalgorithm to remove the unwanted characters from the string:
然后使用std::remove_if算法从字符串中删除不需要的字符：
std::string s = "my data";
s.erase(std::remove_if(s.begin(), s.end(), my_predicate), s.end());
Depending on your requirements, you may be able to use one of the Standard Library predicates, like std::isalnum, instead of writing your own predicate (you said you needed to match alphanumeric characters and spaces, so perhaps this doesn't exactly fit what you need).
根据您的要求，您可以使用标准库谓词之一，例如std::isalnum，而不是编写自己的谓词（您说您需要匹配字母数字字符和空格，所以这可能不完全符合您的需要） .
If you want to use the Standard Library std::isalnumfunction, you will need a cast to disambiguate between the std::isalnumfunction in the C Standard Library header <cctype>(which is the one you want to use) and the std::isalnumin the C++ Standard Library header <locale>(which is not the one you want to use, unless you want to perform locale-specific string processing):
如果你想使用标准库std::isalnum函数，你将需要之间铸造的歧义std::isalnum在C标准库头功能<cctype>（这是您要使用的）和std::isalnum在C ++标准库头<locale>（这是不是一个您想使用，除非您想执行特定于语言环境的字符串处理）：
s.erase(std::remove_if(s.begin(), s.end(), (int(*)(int))std::isalnum), s.end());
This works equally well with any of the sequence containers (including std::string, std::vectorand std::deque). This idiom is commonly referred to as the "erase/remove" idiom. The std::remove_ifalgorithm will also work with ordinary arrays. The std::remove_ifmakes only a single pass over the sequence, so it has linear time complexity.
这同样适用于任何序列容器（包括std::string、std::vector和std::deque）。此习语通常称为“擦除/删除”习语。该std::remove_if算法也适用于普通数组。在std::remove_if使得仅在序列的单通，所以它有线性时间复杂度。
回答by Dado
Previous uses of std::isalnumwon't compile with std::ptr_funwithout passing the unaryargument is requires, hence this solution with a lambda function should encapsulate the correct answer:
以前使用的std::isalnum不会在std::ptr_fun不传递一元参数的情况下编译是需要的，因此这个带有 lambda 函数的解决方案应该封装正确的答案：
s.erase(std::remove_if(s.begin(), s.end(),
[]( auto const& c ) -> bool { return !std::isalnum(c); } ), s.end());
回答by Seth Carnegie
You could always loop through and just eraseall non alphanumeric characters if you're using string.
你可以通过始终循环只是erase，如果你正在使用的所有非字母数字字符string。
#include <cctype>
size_t i = 0;
size_t len = str.length();
while(i < len){
if (!isalnum(str[i]) || str[i] == ' '){
str.erase(i,1);
len--;
}else
i++;
}
Someone better with the Standard Lib can probably do this without a loop.
更好地使用标准库的人可能可以在没有循环的情况下做到这一点。
If you're using just a charbuffer, you can loop through and if a character is not alphanumeric, shift all the characters after it backwards one (to overwrite the offending character):
如果您只使用char缓冲区，则可以循环遍历，如果字符不是字母数字，则将其后的所有字符向后移动一个（以覆盖有问题的字符）：
#include <cctype>
size_t buflen = something;
for (size_t i = 0; i < buflen; ++i)
if (!isalnum(buf[i]) || buf[i] != ' ')
memcpy(buf[i], buf[i + 1], --buflen - i);
回答by Eugen Constantin Dinca
The remove_copy_ifstandard algorithm would be very appropriate for your case.
该remove_copy_if标准算法将非常适合您的情况。
回答by TankorSmash
#include <cctype>
#include <string>
#include <functional>
std::string s = "Hello World!";
s.erase(std::remove_if(s.begin(), s.end(),
std::not1(std::ptr_fun(std::isalnum)), s.end()), s.end());
std::cout << s << std::endl;
Results in:
结果是：
"HelloWorld"
You use isalnumto determine whether or not each character is alpha numeric, then use ptr_funto pass the function to not1which NOTs the returned value, leaving you with only the alphanumeric stuff you want.
您用于isalnum确定每个字符是否为字母数字，然后用于将返回值非ptr_fun的函数传递给not1您，只留下您想要的字母数字内容。
回答by Ali Eren ?elik
Just extending James McNellis's code a little bit more. His function is deleting alnum characters instead of non-alnum ones.
只是稍微扩展了 James McNellis 的代码。他的功能是删除alnum字符而不是非alnum字符。
To delete non-alnum characters from a string. (alnum = alphabetical or numeric)
从字符串中删除非 anum 字符。（alnum = 字母或数字）
Declare a function (isalnum returns 0 if passed char is not alnum)
bool isNotAlnum(char c) { return isalnum(c) == 0; }And then write this
s.erase(remove_if(s.begin(), s.end(), isNotAlnum), s.end());
声明一个函数（如果传入的字符不是 alnum，则 isalnum 返回 0）
bool isNotAlnum(char c) { return isalnum(c) == 0; }然后写这个
s.erase(remove_if(s.begin(), s.end(), isNotAlnum), s.end());
then your string is only with alnum characters.
那么你的字符串只有 alnum 字符。
回答by Dhruv Kakadiya
Below code should work just fine for given string s. It's utilizing <algorithm>and <locale>libraries.
下面的代码对于给定的 string 应该可以正常工作s。它正在利用<algorithm>和<locale>图书馆。
std::string s("He!!llo Wo,@rld! 12 453");
s.erase(std::remove_if(s.begin(), s.end(), [](char c) { return !std::isalnum(c); }), s.end());
回答by Andres Hurtis
The mentioned solution
提到的解决方案
s.erase( std::remove_if(s.begin(), s.end(), &std::ispunct), s.end());
is very nice, but unfortunately doesn't work with characters like '?' in Visual Studio (debug mode), because of this line:
非常好，但不幸的是不适用于像“？”这样的字符 在 Visual Studio（调试模式）中，因为这一行：
_ASSERTE((unsigned)(c + 1) <= 256)
in isctype.c
在 isctype.c 中
So, I would recommend something like this:
所以，我会推荐这样的东西：
inline int my_ispunct( int ch )
{
return std::ispunct(unsigned char(ch));
}
...
s.erase( std::remove_if(s.begin(), s.end(), &my_ispunct), s.end());
回答by akritaag
You can use the remove-erase algorithm this way -
您可以通过这种方式使用删除擦除算法 -
// Removes all punctuation
s.erase( std::remove_if(s.begin(), s.end(), &ispunct), s.end());
回答by Pabitra Dash
The following works for me.
以下对我有用。
str.erase(std::remove_if(str.begin(), str.end(), &ispunct), str.end());
str.erase(std::remove_if(str.begin(), str.end(), &isspace), str.end());
