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

这里有许多过于复杂的建议。试试这个简单的std::string解决方案:

using namespace std;

string someText = ...

string::size_type tokenOff = 0, sepOff = tokenOff;
while (sepOff != string::npos)
{
    sepOff = someText.find(' ', sepOff);
    string::size_type tokenLen = (sepOff == string::npos) ? sepOff : sepOff++ - tokenOff;
    string token = someText.substr(tokenOff, tokenLen);
    if (!token.empty())
        /* do something with token */;
    tokenOff = sepOff;
}

其他回答

我以前只用标准库做了一个lexer/tokenizer。代码如下:

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

using namespace std;

string seps(string& s) {
    if (!s.size()) return "";
    stringstream ss;
    ss << s[0];
    for (int i = 1; i < s.size(); i++) {
        ss << '|' << s[i];
    }
    return ss.str();
}

void Tokenize(string& str, vector<string>& tokens, const string& delimiters = " ")
{
    seps(str);

    // Skip delimiters at beginning.
    string::size_type lastPos = str.find_first_not_of(delimiters, 0);
    // Find first "non-delimiter".
    string::size_type pos = str.find_first_of(delimiters, lastPos);

    while (string::npos != pos || string::npos != lastPos)
    {
        // Found a token, add it to the vector.
        tokens.push_back(str.substr(lastPos, pos - lastPos));
        // Skip delimiters.  Note the "not_of"
        lastPos = str.find_first_not_of(delimiters, pos);
        // Find next "non-delimiter"
        pos = str.find_first_of(delimiters, lastPos);
    }
}

int main(int argc, char *argv[])
{
    vector<string> t;
    string s = "Tokens for everyone!";

    Tokenize(s, t, "|");

    for (auto c : t)
        cout << c << endl;

    system("pause");

    return 0;
}

如果你愿意使用C语言,你可以使用strtok函数。在使用它时,您应该注意多线程问题。

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。

这是一个非常简单的问题:

#include <vector>
#include <string>
using namespace std;

vector<string> split(const char *str, char c = ' ')
{
    vector<string> result;

    do
    {
        const char *begin = str;

        while(*str != c && *str)
            str++;

        result.push_back(string(begin, str));
    } while (0 != *str++);

    return result;
}

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