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
我的实施可以是另一种解决方案：
std::vector<std::wstring> SplitString(const std::wstring & String, const std::wstring & Seperator)
{
std::vector<std::wstring> Lines;
size_t stSearchPos = 0;
size_t stFoundPos;
while (stSearchPos < String.size() - 1)
{
stFoundPos = String.find(Seperator, stSearchPos);
stFoundPos = (stFoundPos == std::string::npos) ? String.size() : stFoundPos;
Lines.push_back(String.substr(stSearchPos, stFoundPos - stSearchPos));
stSearchPos = stFoundPos + Seperator.size();
}
return Lines;
}
测试代码：
std::wstring MyString(L"Part 1SEPsecond partSEPlast partSEPend");
std::vector<std::wstring> Parts = IniFile::SplitString(MyString, L"SEP");
std::wcout << L"The string: " << MyString << std::endl;
for (std::vector<std::wstring>::const_iterator it=Parts.begin(); it<Parts.end(); ++it)
{
std::wcout << *it << L"<---" << std::endl;
}
std::wcout << std::endl;
MyString = L"this,time,a,comma separated,string";
std::wcout << L"The string: " << MyString << std::endl;
Parts = IniFile::SplitString(MyString, L",");
for (std::vector<std::wstring>::const_iterator it=Parts.begin(); it<Parts.end(); ++it)
{
std::wcout << *it << L"<---" << std::endl;
}
测试代码的输出：
The string: Part 1SEPsecond partSEPlast partSEPend
Part 1<---
second part<---
last part<---
end<---
The string: this,time,a,comma separated,string
this<---
time<---
a<---
comma separated<---
string<---
其他回答
并不是说我们需要更多的答案，但这是我受到埃文·特兰启发后想到的。
std::vector <std::string> split(const string &input, auto delimiter, bool skipEmpty=true) {
/*
Splits a string at each delimiter and returns these strings as a string vector.
If the delimiter is not found then nothing is returned.
If skipEmpty is true then strings between delimiters that are 0 in length will be skipped.
*/
bool delimiterFound = false;
int pos=0, pPos=0;
std::vector <std::string> result;
while (true) {
pos = input.find(delimiter,pPos);
if (pos != std::string::npos) {
if (skipEmpty==false or pos-pPos > 0) // if empty values are to be kept or not
result.push_back(input.substr(pPos,pos-pPos));
delimiterFound = true;
} else {
if (pPos < input.length() and delimiterFound) {
if (skipEmpty==false or input.length()-pPos > 0) // if empty values are to be kept or not
result.push_back(input.substr(pPos,input.length()-pPos));
}
break;
}
pPos = pos+1;
}
return result;
}
在处理空格作为分隔符时，使用std:：istream_iterator<T>的明显答案已经给出，并得到了很多支持。当然，元素可能不是用空格分隔，而是用一些分隔符分隔。我没有找到任何答案，只是重新定义了空格的含义，将其称为分隔符，然后使用常规方法。
要改变流对空白的看法，只需使用（std:：istream:：imbue（））将流的std:：locale更改为std:：ctype<char>方面，并定义空白的含义（也可以对std:：：ctype<wchar_t>进行更改，但实际上略有不同，因为std:：actype<char>是表驱动的，而std:：type<wchar_t>是由虚拟函数驱动的）。
#include <iostream>
#include <algorithm>
#include <iterator>
#include <sstream>
#include <locale>
struct whitespace_mask {
std::ctype_base::mask mask_table[std::ctype<char>::table_size];
whitespace_mask(std::string const& spaces) {
std::ctype_base::mask* table = this->mask_table;
std::ctype_base::mask const* tab
= std::use_facet<std::ctype<char>>(std::locale()).table();
for (std::size_t i(0); i != std::ctype<char>::table_size; ++i) {
table[i] = tab[i] & ~std::ctype_base::space;
}
std::for_each(spaces.begin(), spaces.end(), [=](unsigned char c) {
table[c] |= std::ctype_base::space;
});
}
};
class whitespace_facet
: private whitespace_mask
, public std::ctype<char> {
public:
whitespace_facet(std::string const& spaces)
: whitespace_mask(spaces)
, std::ctype<char>(this->mask_table) {
}
};
struct whitespace {
std::string spaces;
whitespace(std::string const& spaces): spaces(spaces) {}
};
std::istream& operator>>(std::istream& in, whitespace const& ws) {
std::locale loc(in.getloc(), new whitespace_facet(ws.spaces));
in.imbue(loc);
return in;
}
// everything above would probably go into a utility library...
int main() {
std::istringstream in("a, b, c, d, e");
std::copy(std::istream_iterator<std::string>(in >> whitespace(", ")),
std::istream_iterator<std::string>(),
std::ostream_iterator<std::string>(std::cout, "\n"));
std::istringstream pipes("a b c| d |e e");
std::copy(std::istream_iterator<std::string>(pipes >> whitespace("|")),
std::istream_iterator<std::string>(),
std::ostream_iterator<std::string>(std::cout, "\n"));
}
大部分代码用于打包提供软分隔符的通用工具：合并一行中的多个分隔符。无法生成空序列。当流中需要不同的分隔符时，您可能会使用共享流缓冲区使用不同的设置流：
void f(std::istream& in) {
std::istream pipes(in.rdbuf());
pipes >> whitespace("|");
std::istream comma(in.rdbuf());
comma >> whitespace(",");
std::string s0, s1;
if (pipes >> s0 >> std::ws // read up to first pipe and ignore sequence of pipes
&& comma >> s1 >> std::ws) { // read up to first comma and ignore commas
// ...
}
}
我对string和u32string~的一般实现，使用boost:：algorithm：：split签名。
template<typename CharT, typename UnaryPredicate>
void split(std::vector<std::basic_string<CharT>>& split_result,
const std::basic_string<CharT>& s,
UnaryPredicate predicate)
{
using ST = std::basic_string<CharT>;
using std::swap;
std::vector<ST> tmp_result;
auto iter = s.cbegin(),
end_iter = s.cend();
while (true)
{
/**
* edge case: empty str -> push an empty str and exit.
*/
auto find_iter = find_if(iter, end_iter, predicate);
tmp_result.emplace_back(iter, find_iter);
if (find_iter == end_iter) { break; }
iter = ++find_iter;
}
swap(tmp_result, split_result);
}
template<typename CharT>
void split(std::vector<std::basic_string<CharT>>& split_result,
const std::basic_string<CharT>& s,
const std::basic_string<CharT>& char_candidate)
{
std::unordered_set<CharT> candidate_set(char_candidate.cbegin(),
char_candidate.cend());
auto predicate = [&candidate_set](const CharT& c) {
return candidate_set.count(c) > 0U;
};
return split(split_result, s, predicate);
}
template<typename CharT>
void split(std::vector<std::basic_string<CharT>>& split_result,
const std::basic_string<CharT>& s,
const CharT* literals)
{
return split(split_result, s, std::basic_string<CharT>(literals));
}
没有任何内存分配的C++17版本（std:：函数除外）
void iter_words(const std::string_view& input, const std::function<void(std::string_view)>& process_word) {
auto itr = input.begin();
auto consume_whitespace = [&]() {
for(; itr != input.end(); ++itr) {
if(!isspace(*itr))
return;
}
};
auto consume_letters = [&]() {
for(; itr != input.end(); ++itr) {
if(isspace(*itr))
return;
}
};
while(true) {
consume_whitespace();
if(itr == input.end())
return;
auto word_start = itr - input.begin();
consume_letters();
auto word_end = itr - input.begin();
process_word(input.substr(word_start, word_end - word_start));
}
}
int main() {
iter_words("foo bar", [](std::string_view sv) {
std::cout << "Got word: " << sv << '\n';
});
return 0;
}
我喜欢下面的代码，因为它将结果放入一个向量中，支持字符串作为delim，并控制保持空值。但是，那时候看起来不太好。
#include <ostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
using namespace std;
vector<string> split(const string& s, const string& delim, const bool keep_empty = true) {
vector<string> result;
if (delim.empty()) {
result.push_back(s);
return result;
}
string::const_iterator substart = s.begin(), subend;
while (true) {
subend = search(substart, s.end(), delim.begin(), delim.end());
string temp(substart, subend);
if (keep_empty || !temp.empty()) {
result.push_back(temp);
}
if (subend == s.end()) {
break;
}
substart = subend + delim.size();
}
return result;
}
int main() {
const vector<string> words = split("So close no matter how far", " ");
copy(words.begin(), words.end(), ostream_iterator<string>(cout, "\n"));
}
当然，Boost有一个split（），它的部分功能与此类似。而且，如果“空白”是指任何类型的空白，那么使用Boost的split和is_any_of（）都非常有用。
