Java有一个方便的分割方法:

String str = "The quick brown fox";
String[] results = str.split(" ");

在c++中有简单的方法来做到这一点吗?


当前回答

MFC/ATL有一个非常好的标记器。从MSDN:

CAtlString str( "%First Second#Third" );
CAtlString resToken;
int curPos= 0;

resToken= str.Tokenize("% #",curPos);
while (resToken != "")
{
   printf("Resulting token: %s\n", resToken);
   resToken= str.Tokenize("% #",curPos);
};

Output

Resulting Token: First
Resulting Token: Second
Resulting Token: Third

其他回答

在我看来很奇怪的是,SO网站上有这么多注重速度的书呆子,却没有人给出一个使用编译时生成的分隔符查找表的版本(下面是示例实现)。使用查找表和迭代器应该在效率上击败std::regex,如果你不需要击败regex,就使用它,它是c++ 11的标准,超级灵活。

有些人已经建议使用正则表达式,但对于新手来说,这里有一个打包的示例,应该完全符合OP的期望:

std::vector<std::string> split(std::string::const_iterator it, std::string::const_iterator end, std::regex e = std::regex{"\\w+"}){
    std::smatch m{};
    std::vector<std::string> ret{};
    while (std::regex_search (it,end,m,e)) {
        ret.emplace_back(m.str());              
        std::advance(it, m.position() + m.length()); //next start position = match position + match length
    }
    return ret;
}
std::vector<std::string> split(const std::string &s, std::regex e = std::regex{"\\w+"}){  //comfort version calls flexible version
    return split(s.cbegin(), s.cend(), std::move(e));
}
int main ()
{
    std::string str {"Some people, excluding those present, have been compile time constants - since puberty."};
    auto v = split(str);
    for(const auto&s:v){
        std::cout << s << std::endl;
    }
    std::cout << "crazy version:" << std::endl;
    v = split(str, std::regex{"[^e]+"});  //using e as delim shows flexibility
    for(const auto&s:v){
        std::cout << s << std::endl;
    }
    return 0;
}

如果我们需要更快并接受所有字符必须为8位的约束,我们可以在编译时使用元编程创建一个查找表:

template<bool...> struct BoolSequence{};        //just here to hold bools
template<char...> struct CharSequence{};        //just here to hold chars
template<typename T, char C> struct Contains;   //generic
template<char First, char... Cs, char Match>    //not first specialization
struct Contains<CharSequence<First, Cs...>,Match> :
    Contains<CharSequence<Cs...>, Match>{};     //strip first and increase index
template<char First, char... Cs>                //is first specialization
struct Contains<CharSequence<First, Cs...>,First>: std::true_type {}; 
template<char Match>                            //not found specialization
struct Contains<CharSequence<>,Match>: std::false_type{};

template<int I, typename T, typename U> 
struct MakeSequence;                            //generic
template<int I, bool... Bs, typename U> 
struct MakeSequence<I,BoolSequence<Bs...>, U>:  //not last
    MakeSequence<I-1, BoolSequence<Contains<U,I-1>::value,Bs...>, U>{};
template<bool... Bs, typename U> 
struct MakeSequence<0,BoolSequence<Bs...>,U>{   //last  
    using Type = BoolSequence<Bs...>;
};
template<typename T> struct BoolASCIITable;
template<bool... Bs> struct BoolASCIITable<BoolSequence<Bs...>>{
    /* could be made constexpr but not yet supported by MSVC */
    static bool isDelim(const char c){
        static const bool table[256] = {Bs...};
        return table[static_cast<int>(c)];
    }   
};
using Delims = CharSequence<'.',',',' ',':','\n'>;  //list your custom delimiters here
using Table = BoolASCIITable<typename MakeSequence<256,BoolSequence<>,Delims>::Type>;

有了这些,创建getNextToken函数就很容易了:

template<typename T_It>
std::pair<T_It,T_It> getNextToken(T_It begin,T_It end){
    begin = std::find_if(begin,end,std::not1(Table{})); //find first non delim or end
    auto second = std::find_if(begin,end,Table{});      //find first delim or end
    return std::make_pair(begin,second);
}

使用它也很简单:

int main() {
    std::string s{"Some people, excluding those present, have been compile time constants - since puberty."};
    auto it = std::begin(s);
    auto end = std::end(s);
    while(it != std::end(s)){
        auto token = getNextToken(it,end);
        std::cout << std::string(token.first,token.second) << std::endl;
        it = token.second;
    }
    return 0;
}

这里有一个生动的例子:http://ideone.com/GKtkLQ

对于简单的事情,我只使用以下方法:

unsigned TokenizeString(const std::string& i_source,
                        const std::string& i_seperators,
                        bool i_discard_empty_tokens,
                        std::vector<std::string>& o_tokens)
{
    unsigned prev_pos = 0;
    unsigned pos = 0;
    unsigned number_of_tokens = 0;
    o_tokens.clear();
    pos = i_source.find_first_of(i_seperators, pos);
    while (pos != std::string::npos)
    {
        std::string token = i_source.substr(prev_pos, pos - prev_pos);
        if (!i_discard_empty_tokens || token != "")
        {
            o_tokens.push_back(i_source.substr(prev_pos, pos - prev_pos));
            number_of_tokens++;
        }

        pos++;
        prev_pos = pos;
        pos = i_source.find_first_of(i_seperators, pos);
    }

    if (prev_pos < i_source.length())
    {
        o_tokens.push_back(i_source.substr(prev_pos));
        number_of_tokens++;
    }

    return number_of_tokens;
}

懦弱的免责声明:我编写实时数据处理软件,其中数据通过二进制文件、套接字或一些API调用(I/O卡、摄像头)传入。除了在启动时读取外部配置文件以外,我从未将这个函数用于更复杂或时间要求更严格的事情。

请看这个例子。它可能对你有帮助。

#include <iostream>
#include <sstream>

using namespace std;

int main ()
{
    string tmps;
    istringstream is ("the dellimiter is the space");
    while (is.good ()) {
        is >> tmps;
        cout << tmps << "\n";
    }
    return 0;
}

简单的c++代码(标准c++ 98),接受多个分隔符(在std::string中指定),只使用向量、字符串和迭代器。

#include <iostream>
#include <vector>
#include <string>
#include <stdexcept> 

std::vector<std::string> 
split(const std::string& str, const std::string& delim){
    std::vector<std::string> result;
    if (str.empty())
        throw std::runtime_error("Can not tokenize an empty string!");
    std::string::const_iterator begin, str_it;
    begin = str_it = str.begin(); 
    do {
        while (delim.find(*str_it) == std::string::npos && str_it != str.end())
            str_it++; // find the position of the first delimiter in str
        std::string token = std::string(begin, str_it); // grab the token
        if (!token.empty()) // empty token only when str starts with a delimiter
            result.push_back(token); // push the token into a vector<string>
        while (delim.find(*str_it) != std::string::npos && str_it != str.end())
            str_it++; // ignore the additional consecutive delimiters
        begin = str_it; // process the remaining tokens
        } while (str_it != str.end());
    return result;
}

int main() {
    std::string test_string = ".this is.a.../.simple;;test;;;END";
    std::string delim = "; ./"; // string containing the delimiters
    std::vector<std::string> tokens = split(test_string, delim);           
    for (std::vector<std::string>::const_iterator it = tokens.begin(); 
        it != tokens.end(); it++)
            std::cout << *it << std::endl;
}

这是一个简单的循环,只对标准库文件进行标记

#include <iostream.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <conio.h>
class word
    {
     public:
     char w[20];
     word()
      {
        for(int j=0;j<=20;j++)
        {w[j]='\0';
      }
   }



};

void main()
  {
    int i=1,n=0,j=0,k=0,m=1;
    char input[100];
    word ww[100];
    gets(input);

    n=strlen(input);


    for(i=0;i<=m;i++)
      {
        if(context[i]!=' ')
         {
            ww[k].w[j]=context[i];
            j++;

         }
         else
        {
         k++;
         j=0;
         m++;
        }

   }
 }