[英]Is There a Way to Discard Empty Captures?
Is there a built in way to iterate over non-empty captures only or do I need to use a lambda/modify my regex? 是否有内置的方法来迭代非空捕获或我是否需要使用lambda /修改我的正则表达式?
For example, given: const auto input = "Peas&Carrots Spinach-Casserole Beets Pizza Spinach-Salad Coleslaw"s
I'd like to find foods that don't contain "Spinach". 例如,给定:
const auto input = "Peas&Carrots Spinach-Casserole Beets Pizza Spinach-Salad Coleslaw"s
我想找到不包含“菠菜”的食物。 So I can do this: 所以我可以这样做:
const regex re{ "\\s*(?:\\S*Spinach\\S*|(\\S*))" };
copy(sregex_token_iterator(cbegin(input), cend(input), re, 1), sregex_token_iterator(), ostream_iterator<string>(cout, "\n"));
The problem of course is that I get an output like: 问题当然是我得到的输出如下:
Peas&Carrots
豌豆和胡萝卜
Beets甜菜
Pizza比萨
Coleslaw凉拌卷心菜
Is there a way around this? 有没有解决的办法?
The obvious way would be to use std::copy_if
(or std::remove_copy_if
) and copy the string only if it's non-empty. 显而易见的方法是使用
std::copy_if
(或std::remove_copy_if
)并仅在字符串非空时复制字符串。
remove_copy_if(
sregex_token_iterator(cbegin(input), cend(input), re, 1),
sregex_token_iterator(),
ostream_iterator<string>(cout, "\n"),
[](string const &s) { return s.empty(); }
);
You can use std::copy_if
and a lambda to check that the string from the regex match is empty or not. 您可以使用
std::copy_if
和lambda来检查正则表达式匹配中的字符串是否为空。 Using 运用
copy_if(sregex_token_iterator(cbegin(input), cend(input), re, 1),
sregex_token_iterator(), ostream_iterator<string>(cout, "\n"),
[](const std::string& match){ return !match.empty(); });
We get 我们得到了
Peas&Carrots
Beets
Pizza
Coleslaw
As it will only print non-empty strings. 因为它只会打印非空字符串。
From the answers of those wiser than I, it seems that there is in fact no way to discard empty results without a lambda. 从那些比我更聪明的答案中,似乎实际上没有办法在没有lambda的情况下丢弃空结果。 In this question there are a couple alternatives though:
在这个问题中,有几种选择:
const regex re{ "(?:\\s+|^)(?!Spinach)(\\S+)" };
copy(sregex_token_iterator(cbegin(input), cend(input), re, 1), sregex_token_iterator(), ostream_iterator<string>(cout, "\n"));
istream_iterator
and a lambda, this removes a lot of the flexibility of the lambda, but since input
is white-space delimited this is probably the best option: istream_iterator
和lambda,这消除了lambda的很多灵活性,但由于input
是空格分隔的,这可能是最好的选择: istringstream{ input };
copy_if(istream_iterator<string>(cbegin(input), cend(input)), istream_iterator<string>(), ostream_iterator<string>(cout, "\n"), [](const auto& i) { return i.find("Spinach") == string::npos; });
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