C++ split string by line - c++

Question

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 !

Answer 1

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;
}

Answer 2

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.

Answer 3

#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;
}

Answer 4

#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;}
}
We have a string with multiple lines
we split those into an array (vector)
We print out those elements in a for loop

Answer 5

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>>();
}

Answer 6

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;
}