如何解析 C++ 中的逗号分隔字符串，其中一些元素用逗号引用？

Question

我有一个逗号分隔的字符串，我想将它存储在字符串向量中。 字符串和向量是：

string s = "1, 10, 'abc', 'test, 1'";
vector<string> v;

理想情况下，我希望在没有单引号的情况下存储字符串 'abc' 和 'test, 1'，如下所示，但我可以使用单引号来存储它们：

v[0] = "1";
v[1] = "10";
v[2] = "abc";
v[3] = "test, 1";

Answer 1

您需要在这里做的是让自己成为一个解析器，可以按照您的意愿进行解析。 这里我为大家做了一个解析function：

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

vector<string> parse_string(string master) {
    char temp; //the current character
    bool encountered = false; //for checking if there is a single quote
    string curr_parse; //the current string
    vector<string>result; //the return vector

    for (int i = 0; i < master.size(); ++i) { //while still in the string
        temp = master[i]; //current character
        switch (temp) { //switch depending on the character

        case '\'': //if the character is a single quote
            
            if (encountered) encountered = false; //if we already found a single quote, reset encountered
            else encountered = true; //if we haven't found a single quote, set encountered to true
            [[fallthrough]];

        case ',': //if it is a comma

            if (!encountered) { //if we have not found a single quote
                result.push_back(curr_parse); //put our current string into our vector

                curr_parse = ""; //reset the current string
                break; //go to next character
            }//if we did find a single quote, go to the default, and push_back the comma
            [[fallthrough]];

        default: //if it is a normal character
            if (encountered && isspace(temp)) curr_parse.push_back(temp); //if we have found a single quote put the whitespace, we don't care
            else if (isspace(temp)) break; //if we haven't found a single quote, trash the  whitespace and go to the next character
            else if (temp == '\'') break; //if the current character is a single quote, trash it and go to the next character.
            else curr_parse.push_back(temp); //if all of the above failed, put the character into the current string
            break; //go to the next character
        }
    }
    for (int i = 0; i < result.size(); ++i) { 
        if (result[i] == "") result.erase(result.begin() + i);  
        //check that there are no empty strings in the vector
        //if there are, delete them
    }
    return result;
}

这会根据需要解析您的字符串，并返回一个向量。 然后，您可以在程序中使用它：

#include <iostream>
int main() {
    string s = "1, 10, 'abc', 'test, 1'";
    vector<string> v = parse_string(s);

    for (int i = 0; i < v.size(); ++i) {
        cout << v[i] << endl;
    }
}

并正确打印出：

1
10
abc
test, 1

Answer 2

bool nextToken(const string &s, string::size_type &start, string &token)
{
    token.clear();
    
    start = s.find_first_not_of(" \t", start);
    if (start == string::npos)
        return false;
    
    string::size_type end;
    
    if (s[start] == '\'')
    {
        ++start;
        end = s.find('\'', start);
    }
    else
        end = s.find_first_of(" \t,", start);
    
    if (end == string::npos)
    {
        token = s.substr(start);
        start = s.size();
    }
    else
    {
        token = s.substr(start, end-start);
        if ((s[end] != ',') && ((end = s.find(',', end + 1)) == string::npos))
            start = s.size();
        else
            start = end + 1;
    }
    
    return true;
}

string s = "1, 10, 'abc', 'test, 1'", token;
vector<string> v;
 
string::size_type start = 0;
while (nextToken(s, start, token))
    v.push_back(token);

演示

Answer 3

一个合适的解决方案需要一个解析器实现。 如果您需要快速破解，只需编写一个读取 function 的单元格（演示）。 c++14 的std::quoted操纵器在这里有很大帮助。 唯一的问题是机械手需要 stream。 这很容易用istringstream解决 - 请参阅第二个 function。 请注意，您的字符串格式为CELL COMMA CELL COMMA... CELL 。

istream& get_cell(istream& is, string& s)
{
  char c;
  is >> c; // skips ws
  is.unget(); // puts back in the stream the last read character

  if (c == '\'')
    return is >> quoted(s, '\'', '\\'); // the first character of the cell is ' - read quoted
  else
    return getline(is, s, ','), is.unget(); // read unqoted, but put back comma - we need it later, in get function
}


vector<string> get(const string& s)
{
  istringstream iss{ s };
  string cell;
  vector<string> r;
  while (get_cell(iss, cell))
  {
    r.push_back( cell );
    char comma;
    iss >> comma; // expect a cell separator
    if (comma != ',')
      break; // cell separator not found; we are at the end of stream/string - break the loop
  }

  if (char c; iss >> c) // we reached the end of what we understand - probe the end of stream
    throw "ill formed";

  return r;
}

这就是你使用它的方式：

int main()
{
  string s = "1, 10, 'abc', 'test, 1'";
  try
  {
    auto v = get(s);;
  }
  catch (const char* e)
  {
    cout << e;
  }
}