我正在尝试进行某种类型的“字符串扩展”，其中我用数据库中的字符串替换键。标记的格式为{$<key>}。
我正在使用<regex>尝试完成此操作，但我遇到了一些后勤问题。我希望能够在一次传递中替换字符串，但修改字符串（s）可能会使smatch对象中的迭代器失效。
这或多或少是我正在尝试做的事情：
#include <iostream>
#include <map>
#include <regex>
using namespace std;
int main()
{
map<string, string> m;
m.insert(make_pair("severity", "absolute"));
m.insert(make_pair("experience", "nightmare"));
string s = "This is an {$severity} {$experience}!";
static regex e("\\{\\$(.*?)\\}");
sregex_iterator next(s.begin(), s.end(), e);
sregex_iterator end;
for (; next != end; ++next)
{
auto m_itr = m.find(next->str(1));
if (m_itr == m.end())
{
continue;
}
//TODO: replace expansion tags with strings somehow?
cout << (*next).str(0) << ":" << m_itr->second << endl;
}
}
期望的最终结果是s读取：
"This is an absolute nightmare!"
我知道我可以在多次通过中执行此类事情，但这似乎有点野蛮。
我在某处看到boost::regex有一些regex_replace的变体，允许以这种形式使用自定义替换函数：
regex_replace(std::string&, regex, std::string(const smatch&))
但是，我当前的版本(1.55)没有这样的东西。
非常感谢任何帮助！
P.S。我可以使用boost或std，无论哪个都有效！
答案 0 :(得分：1)
所以，除了我8小时前发表的评论：
或许相关：Compiling a simple parser with Boost.Spirit，replacing pieces of string，How to expand environment variables in .ini files using Boost，也许最有趣的是Fast multi-replacement into string
我看到了另外一个方法的空间。如果......您需要根据相同的文本模板进行许多替换，但使用不同的替换地图会怎样？
由于我最近发现了Boost ICL can be useful in mapping regions of input strings，我想在这里做同样的事情。
我使事情非常通用，并使用Spirit进行分析（study）：
template <
typename InputRange,
typename It = typename boost::range_iterator<InputRange const>::type,
typename IntervalSet = boost::icl::interval_set<It> >
IntervalSet study(InputRange const& input) {
using std::begin;
using std::end;
It first(begin(input)), last(end(input));
using namespace boost::spirit::qi;
using boost::spirit::repository::qi::seek;
IntervalSet variables;
parse(first, last, *seek [ raw [ "{$" >> +alnum >> "}" ] ], variables);
return variables;
}
正如您所看到的，我们只返回interval_set<It>而不是进行任何替换，因此我们知道变量的位置。现在这是“智慧”，可用于从替换字符串的映射执行替换：
template <
typename InputRange,
typename Replacements,
typename OutputIterator,
typename StudyMap,
typename It = typename boost::range_iterator<InputRange const>::type
>
OutputIterator perform_replacements(InputRange const& input, Replacements const& m, StudyMap const& wisdom, OutputIterator out)
{
using std::begin;
using std::end;
It current(begin(input));
for (auto& replace : wisdom)
{
It l(lower(replace)),
u(upper(replace));
if (current < l)
out = std::copy(current, l, out);
auto match = m.find({l+2, u-1});
if (match == m.end())
out = std::copy(l, u, out);
else
out = std::copy(begin(match->second), end(match->second), out);
current = u;
}
if (current!=end(input))
out = std::copy(current, end(input), out);
return out;
}
现在，一个简单的测试程序将是这样的：
int main()
{
using namespace std;
string const input = "This {$oops} is an {$severity} {$experience}!\n";
auto const wisdom = study(input);
cout << "Wisdom: ";
for(auto& entry : wisdom)
cout << entry;
auto m = map<string, string> {
{ "severity", "absolute" },
{ "OOPS", "REALLY" },
{ "experience", "nightmare" },
};
ostreambuf_iterator<char> out(cout);
out = '\n';
perform_replacements(input, m, wisdom, out);
// now let's use a case insensitive map, still with the same "study"
map<string, string, ci_less> im { m.begin(), m.end() };
im["eXperience"] = "joy";
perform_replacements(input, im, wisdom, out);
}
打印
Wisdom: {$oops}{$severity}{$experience}
This {$oops} is an absolute nightmare!
This REALLY is an absolute joy!
你可以用输入字符串文字来调用它，使用unordered_map代替替换等。你可以省略wisdom，在这种情况下，实现将动态研究它。 / p>
<强> Live On Coliru
#include <iostream>
#include <map>
#include <boost/regex.hpp>
#include <boost/icl/interval_set.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/repository/include/qi_seek.hpp>
namespace boost { namespace spirit { namespace traits {
template <typename It>
struct assign_to_attribute_from_iterators<icl::discrete_interval<It>, It, void> {
template <typename ... T> static void call(It b, It e, icl::discrete_interval<It>& out) {
out = icl::discrete_interval<It>::right_open(b, e);
}
};
} } }
template <
typename InputRange,
typename It = typename boost::range_iterator<InputRange const>::type,
typename IntervalSet = boost::icl::interval_set<It> >
IntervalSet study(InputRange const& input) {
using std::begin;
using std::end;
It first(begin(input)), last(end(input));
using namespace boost::spirit::qi;
using boost::spirit::repository::qi::seek;
IntervalSet variables;
parse(first, last, *seek [ raw [ "{$" >> +alnum >> "}" ] ], variables);
return variables;
}
template <
typename InputRange,
typename Replacements,
typename OutputIterator,
typename StudyMap,
typename It = typename boost::range_iterator<InputRange const>::type
>
OutputIterator perform_replacements(InputRange const& input, Replacements const& m, StudyMap const& wisdom, OutputIterator out)
{
using std::begin;
using std::end;
It current(begin(input));
for (auto& replace : wisdom)
{
It l(lower(replace)),
u(upper(replace));
if (current < l)
out = std::copy(current, l, out);
auto match = m.find({l+2, u-1});
if (match == m.end())
out = std::copy(l, u, out);
else
out = std::copy(begin(match->second), end(match->second), out);
current = u;
}
if (current!=end(input))
out = std::copy(current, end(input), out);
return out;
}
template <
typename InputRange,
typename Replacements,
typename OutputIterator,
typename It = typename boost::range_iterator<InputRange const>::type
>
OutputIterator perform_replacements(InputRange const& input, Replacements const& m, OutputIterator out) {
return perform_replacements(input, m, study(input), out);
}
// for demo program
#include <boost/algorithm/string.hpp>
struct ci_less {
template <typename S>
bool operator() (S const& a, S const& b) const {
return boost::lexicographical_compare(a, b, boost::is_iless());
}
};
namespace boost { namespace icl {
template <typename It>
static inline std::ostream& operator<<(std::ostream& os, discrete_interval<It> const& i) {
return os << make_iterator_range(lower(i), upper(i));
}
} }
int main()
{
using namespace std;
string const input = "This {$oops} is an {$severity} {$experience}!\n";
auto const wisdom = study(input);
cout << "Wisdom: ";
for(auto& entry : wisdom)
cout << entry;
auto m = map<string, string> {
{ "severity", "absolute" },
{ "OOPS", "REALLY" },
{ "experience", "nightmare" },
};
ostreambuf_iterator<char> out(cout);
out = '\n';
perform_replacements(input, m, wisdom, out);
// now let's use a case insensitive map, still with the same "study"
map<string, string, ci_less> im { m.begin(), m.end() };
im["eXperience"] = "joy";
perform_replacements(input, im, wisdom, out);
}
只要确保替换字符串总是短于{$pattern}字符串（或等长），就可以使用input.begin()作为输出迭代器来调用此函数。
<强> Live On Coliru
string input1 = "This {$803525c8-3ce4-423a-ad25-cc19bbe8422a} is an {$efa72abf-fe96-4983-b373-a35f70551e06} {$8a10abaa-cc0d-47bd-a8e1-34a8aa0ec1ef}!\n",
input2 = input1;
auto m = map<string, string> {
{ "efa72abf-fe96-4983-b373-a35f70551e06", "absolute" },
{ "803525C8-3CE4-423A-AD25-CC19BBE8422A", "REALLY" },
{ "8a10abaa-cc0d-47bd-a8e1-34a8aa0ec1ef", "nightmare" },
};
input1.erase(perform_replacements(input1, m, input1.begin()), input1.end());
map<string, string, ci_less> im { m.begin(), m.end() };
im["8a10abaa-cc0d-47bd-a8e1-34a8aa0ec1ef"] = "joy";
input2.erase(perform_replacements(input2, im, input2.begin()), input2.end());
std::cout << input1
<< input2;
打印
This {$803525c8-3ce4-423a-ad25-cc19bbe8422a} is an absolute nightmare!
This REALLY is an absolute joy!
请注意，您可以（显然）不会再次在同一输入模板上重复使用相同的“智慧”，因为它会被修改。