如何迭代由空格分隔的单词组成的字符串中的单词?

注意,我对C字符串函数或那种字符操作/访问不感兴趣。比起效率,我更喜欢优雅。我当前的解决方案:

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main() {
    string s = "Somewhere down the road";
    istringstream iss(s);

    do {
        string subs;
        iss >> subs;
        cout << "Substring: " << subs << endl;
    } while (iss);
}

当前回答

没有Boost,没有字符串流,只有标准的C库与std::string和std::list:C库函数配合使用,便于分析,C++数据类型便于内存管理。

空白被认为是换行符、制表符和空格的任意组合。空白字符集由wschars变量建立。

#include <string>
#include <list>
#include <iostream>
#include <cstring>

using namespace std;

const char *wschars = "\t\n ";

list<string> split(const string &str)
{
  const char *cstr = str.c_str();
  list<string> out;

  while (*cstr) {                     // while remaining string not empty
    size_t toklen;
    cstr += strspn(cstr, wschars);    // skip leading whitespace
    toklen = strcspn(cstr, wschars);  // figure out token length
    if (toklen)                       // if we have a token, add to list
      out.push_back(string(cstr, toklen));
    cstr += toklen;                   // skip over token
  }

  // ran out of string; return list

  return out;
}

int main(int argc, char **argv)
{
  list<string> li = split(argv[1]);
  for (list<string>::iterator i = li.begin(); i != li.end(); i++)
    cout << "{" << *i << "}" << endl;
  return 0;
}

Run:

$ ./split ""
$ ./split "a"
{a}
$ ./split " a "
{a}
$ ./split " a b"
{a}
{b}
$ ./split " a b c"
{a}
{b}
{c}
$ ./split " a b c d  "
{a}
{b}
{c}
{d}

split的尾部递归版本(本身分裂为两个函数)。除了将字符串推入列表之外,所有对变量的破坏性操作都消失了!

void split_rec(const char *cstr, list<string> &li)
{
  if (*cstr) {
    const size_t leadsp = strspn(cstr, wschars);
    const size_t toklen = strcspn(cstr + leadsp, wschars);

    if (toklen)
      li.push_back(string(cstr + leadsp, toklen));

    split_rec(cstr + leadsp + toklen, li);
  }
}

list<string> split(const string &str)
{
  list<string> out;
  split_rec(str.c_str(), out);
  return out;
}

其他回答

我使用这个simpleton是因为我们得到了字符串类“特殊”(即非标准):

void splitString(const String &s, const String &delim, std::vector<String> &result) {
    const int l = delim.length();
    int f = 0;
    int i = s.indexOf(delim,f);
    while (i>=0) {
        String token( i-f > 0 ? s.substring(f,i-f) : "");
        result.push_back(token);
        f=i+l;
        i = s.indexOf(delim,f);
    }
    String token = s.substring(f);
    result.push_back(token);
}

如果您希望按某些字符分割字符串,可以使用

#include<iostream>
#include<string>
#include<vector>
#include<iterator>
#include<sstream>
#include<string>

using namespace std;
void replaceOtherChars(string &input, vector<char> &dividers)
{
    const char divider = dividers.at(0);
    int replaceIndex = 0;
    vector<char>::iterator it_begin = dividers.begin()+1,
        it_end= dividers.end();
    for(;it_begin!=it_end;++it_begin)
    {
        replaceIndex = 0;
        while(true)
        {
            replaceIndex=input.find_first_of(*it_begin,replaceIndex);
            if(replaceIndex==-1)
                break;
            input.at(replaceIndex)=divider;
        }
    }
}
vector<string> split(string str, vector<char> chars, bool missEmptySpace =true )
{
    vector<string> result;
    const char divider = chars.at(0);
    replaceOtherChars(str,chars);
    stringstream stream;
    stream<<str;    
    string temp;
    while(getline(stream,temp,divider))
    {
        if(missEmptySpace && temp.empty())
            continue;
        result.push_back(temp);
    }
    return result;
}
int main()
{
    string str ="milk, pigs.... hot-dogs ";
    vector<char> arr;
    arr.push_back(' '); arr.push_back(','); arr.push_back('.');
    vector<string> result = split(str,arr);
    vector<string>::iterator it_begin= result.begin(),
        it_end= result.end();
    for(;it_begin!=it_end;++it_begin)
    {
        cout<<*it_begin<<endl;
    }
return 0;
}

使用std::string_view和Eric Niebler的range-v3库:

https://wandbox.org/permlink/kW5lwRCL1pxjp2pW

#include <iostream>
#include <string>
#include <string_view>
#include "range/v3/view.hpp"
#include "range/v3/algorithm.hpp"

int main() {
    std::string s = "Somewhere down the range v3 library";
    ranges::for_each(s  
        |   ranges::view::split(' ')
        |   ranges::view::transform([](auto &&sub) {
                return std::string_view(&*sub.begin(), ranges::distance(sub));
            }),
        [](auto s) {std::cout << "Substring: " << s << "\n";}
    );
}

通过使用循环的范围而不是范围::for_each算法:

#include <iostream>
#include <string>
#include <string_view>
#include "range/v3/view.hpp"

int main()
{
    std::string str = "Somewhere down the range v3 library";
    for (auto s : str | ranges::view::split(' ')
                      | ranges::view::transform([](auto&& sub) { return std::string_view(&*sub.begin(), ranges::distance(sub)); }
                      ))
    {
        std::cout << "Substring: " << s << "\n";
    }
}

这是我最喜欢的遍历字符串的方法。每个词你都可以做你想做的事。

string line = "a line of text to iterate through";
string word;

istringstream iss(line, istringstream::in);

while( iss >> word )     
{
    // Do something on `word` here...
}

还有另一种方式——连续传递方式、零分配、基于函数的分隔。

 void split( auto&& data, auto&& splitter, auto&& operation ) {
   using std::begin; using std::end;
   auto prev = begin(data);
   while (prev != end(data) ) {
     auto&&[prev,next] = splitter( prev, end(data) );
     operation(prev,next);
     prev = next;
   }
 }

现在我们可以基于此编写特定的拆分函数。

 auto anyOfSplitter(auto delimiters) {
   return [delimiters](auto begin, auto end) {
     while( begin != end && 0 == std::string_view(begin, end).find_first_of(delimiters) ) {
       ++begin;
     }
     auto view = std::string_view(begin, end);
     auto next = view.find_first_of(delimiters);
     if (next != view.npos)
       return std::make_pair( begin, begin + next );
     else
       return std::make_pair( begin, end );
   };
 }

我们现在可以生成一个传统的std字符串分割,如下所示:

 template<class C>
 auto traditional_any_of_split( std::string_view<C> str, std::string_view<C> delim ) {
   std::vector<std::basic_string<C>> retval;
   split( str, anyOfSplitter(delim), [&](auto s, auto f) {
     retval.emplace_back(s,f);
   });
   return retval;
 }

或者我们可以改用find

 auto findSplitter(auto delimiter) {
   return [delimiter](auto begin, auto end) {
     while( begin != end && 0 == std::string_view(begin, end).find(delimiter) ) {
       begin += delimiter.size();
     }
     auto view = std::string_view(begin, end);
     auto next = view.find(delimiter);
     if (next != view.npos)
       return std::make_pair( begin, begin + next );
     else
       return std::make_pair( begin, end );
   };
 }

 template<class C>
 auto traditional_find_split( std::string_view<C> str, std::string_view<C> delim ) {
   std::vector<std::basic_string<C>> retval;
   split( str, findSplitter(delim), [&](auto s, auto f) {
     retval.emplace_back(s,f);
   });
   return retval;
 }

通过更换分流器部分。

这两者都分配了一个返回值缓冲区。我们可以以手动管理生命周期为代价将返回值交换到字符串视图。

我们还可以采用一个延续,一次传递一个字符串视图,甚至避免分配视图向量。

这可以通过一个中止选项进行扩展,这样我们可以在读取几个前缀字符串后中止。