CODEWITHSUNDEEP
c++split
wangzhiju
wangzhiju

Reputation: 855

C++ split string by line

I need to split string by line. I used to do in the following way:

int doSegment(char *sentence, int segNum)
{
assert(pSegmenter != NULL);
Logger &log = Logger::getLogger();
char delims[] = "\n";
char *line = NULL;
if (sentence != NULL)
{
    line = strtok(sentence, delims);
    while(line != NULL)
    {
        cout << line << endl;
        line = strtok(NULL, delims);
    }
}
else
{
    log.error("....");
}
return 0;
}

I input "we are one.\nyes we are." and invoke the doSegment method. But when i debugging, i found the sentence parameter is "we are one.\\nyes we are", and the split failed. Can somebody tell me why this happened and what should i do. Is there anyway else i can use to split string in C++. thanks !

Upvotes: 47

Views: 103277

Answers (6)

Oleksandr Kozlov
Oleksandr Kozlov

Reputation: 755

Using the library range-v3:

#include <range/v3/all.hpp>
#include <string>
#include <string_view>
#include <vector>

std::vector<std::string> split_string_by_newline(const std::string_view str) {
  return str | ranges::views::split('\n')
             | ranges::to<std::vector<std::string>>();
}

Using C++23 ranges:

#include <ranges>
#include <string>
#include <string_view>
#include <vector>

std::vector<std::string> split_string_by_newline(const std::string_view str) {
  return str | std::ranges::views::split('\n')
             | std::ranges::to<std::vector<std::string>>();
}

Upvotes: 2

Some programmer dude
Some programmer dude

Reputation: 409166

You can call std::string::find in a loop and the use std::string::substr.

std::vector<std::string> split_string(const std::string& str,
                                      const std::string& delimiter)
{
    std::vector<std::string> strings;

    std::string::size_type pos = 0;
    std::string::size_type prev = 0;
    while ((pos = str.find(delimiter, prev)) != std::string::npos)
    {
        strings.push_back(str.substr(prev, pos - prev));
        prev = pos + delimiter.size();
    }

    // To get the last substring (or only, if delimiter is not found)
    strings.push_back(str.substr(prev));

    return strings;
}

See example here.

Upvotes: 22

Oleksandr Kozlov
Oleksandr Kozlov

Reputation: 755

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

std::vector<std::string> split_string_by_newline(const std::string& str)
{
    auto result = std::vector<std::string>{};
    auto ss = std::stringstream{str};

    for (std::string line; std::getline(ss, line, '\n');)
        result.push_back(line);

    return result;
}

Upvotes: 20

Scourge
Scourge

Reputation: 71

#include <iostream>
#include <string>
#include <regex>
#include <algorithm>
#include <iterator>
    
using namespace std;


vector<string> splitter(string in_pattern, string& content){
    vector<string> split_content;

    regex pattern(in_pattern);
    copy( sregex_token_iterator(content.begin(), content.end(), pattern, -1),
    sregex_token_iterator(),back_inserter(split_content));  
    return split_content;
}
    
int main()
{   

    string sentence = "This is the first line\n";
    sentence += "This is the second line\n";
    sentence += "This is the third line\n";

    vector<string> lines = splitter(R"(\n)", sentence);

    for (string line: lines){cout << line << endl;}

}
  1. We have a string with multiple lines
  2. we split those into an array (vector)
  3. We print out those elements in a for loop

Upvotes: 1

Jelle Jan
Jelle Jan

Reputation: 156

This fairly inefficient way just loops through the string until it encounters an \n newline escape character. It then creates a substring and adds it to a vector.

std::vector<std::string> Loader::StringToLines(std::string string)
{
    std::vector<std::string> result;
    std::string temp;
    int markbegin = 0;
    int markend = 0;

    for (int i = 0; i < string.length(); ++i) {     
        if (string[i] == '\n') {
            markend = i;
            result.push_back(string.substr(markbegin, markend - markbegin));
            markbegin = (i + 1);
        }
    }
    return result;
}

Upvotes: -1

billz
billz

Reputation: 45410

I'd like to use std::getline or std::string::find to go through the string. below code demonstrates getline function

int doSegment(char *sentence)
{
  std::stringstream ss(sentence);
  std::string to;

  if (sentence != NULL)
  {
    while(std::getline(ss,to,'\n')){
      cout << to <<endl;
    }
  }

return 0;
}

Upvotes: 84

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