ignore punctuation using manipulator
Is it possibile to ignore punctuacion using std manipulator on cin? For example suppose you have an input stream (in the actual case a file) like: "one, two three". I want to be able to do:
f >> ignore_punct >> a;
f >> ignore_punct >> b;
f >开发者_高级运维> ignore_punct >> c;
at the end a=="one"
, b=="two"
, c=="three"
.
Try this:
It uses the local to filter out punctuation.
This allows the rest of the code to remain unchanged.
#include <locale>
#include <string>
#include <iostream>
#include <fstream>
#include <cctype>
class PunctRemove: public std::codecvt<char,char,std::char_traits<char>::state_type>
{
bool do_always_noconv() const throw() { return false;}
int do_encoding() const throw() { return true; }
typedef std::codecvt<char,char,std::char_traits<char>::state_type> MyType;
typedef MyType::state_type state_type;
typedef MyType::result result;
virtual result do_in(state_type& s,
const char* from,const char* from_end,const char*& from_next,
char* to, char* to_limit, char*& to_next ) const
{
/*
* This function is used to filter the input
*/
for(from_next = from, to_next = to;from_next != from_end;++from_next)
{
if (!std::ispunct(*from_next))
{
*to_next = *from_from;
++to_next;
}
}
return ok;
}
/*
* This function is used to filter the output
*/
virtual result do_out(state_type& state,
const char* from, const char* from_end, const char*& from_next,
char* to, char* to_limit, char*& to_next ) const
{ /* I think you can guess this */ }
};
int main()
{
// stream must be imbued before they are opened.
// Otherwise the imbing is ignored.
//
std::ifstream data;
data.imbue(std::locale(std::locale(), new PunctRemove));
data.open("plop");
if (!data)
{
std::cout << "Failed to open plop\n";
return 1;
}
std::string line;
std::getline(data, line);
std::cout << "L(" << line << ")\n";
}
There's no standard-library way to do it, but it's pretty easy to do, if I understand you correctly. If you want to read a string until some punctuation as though it were a newline, then you could use a version of getline
that accepts a predicate instead of a single delimiter:
template<class F>
std::istream& getline(std::istream& stream, std::string& string, F delim) {
string.clear();
// Get characters while the stream is valid and the next character is not the terminating delimiter.
while (stream && !delim(stream.peek()))
string += stream.get();
// Discard delimiter.
stream.ignore(1);
return stream;
};
Usage example:
#include <iostream>
#include <cctype>
int main(int argc, char** argv) {
std::string s;
getline(std::cin, s, ::ispunct);
std::cout << s << '\n';
return 0;
}
If you also want to break on newlines, then you can write a functor:
struct punct_or_newline {
bool operator()(char c) const { return ::ispunct(c) || c == '\n'; }
};
And invoke as getline(std::cin, my_string, punct_or_newline())
instead. Hope this helps!
精彩评论