Parsing a string in c++ with a specfic format - c++

Question

I have this string post "ola tudo bem como esta" alghero.jpg and i want to break it into 3 pieces post, ola tudo bem como esta (i dont want the "") and alghero.jpg i tried it in c because im new and not really good at programming in c++ but its not working. Is there a more efficient way of doing this in c++?
Program:
int main()
{
char* token1 = new char[128];
char* token2 = new char[128];
char* token3 = new char[128];
char str[] = "post \"ola tudo bem como esta\" alghero.jpg";
char *token;
/* get the first token */
token = strtok(str, " ");
//walk through other tokens
while( token != NULL ) {
printf( " %s\n", token );
token = strtok(NULL, " ");
}
return(0);
}

Answer 1

In C++14 and later, you can use std::quoted to read quoted strings from any std::istream, such as std::istringstream, eg:
#include <iostream>
#include <sstream>
#include <string>
#include <iomanip>
int main()
{
std::string token1, token2, token3;
std::string str = "post \"ola tudo bem como esta\" alghero.jpg";
std::istringstream(str) >> token1 >> std::quoted(token2) >> token3;
std::cout << token1 << "\n";
std::cout << token2 << "\n";
std::cout << token3 << "\n";
return 0;
}

Answer 2

Use find to find the positions of the 2 quotes. Use substr to get the string from index 0 to first quote, first quote to second quote, and second quote to end.
std::string s = "post \"ola tudo bem como esta\" alghero.jpg";
auto first = s.find('\"');
if (first != s.npos) {
auto second = s.find('\"', first + 1);
if (second != s.npos) {
std::cout << s.substr(0, first-1) << '\n';
std::cout << s.substr(first+1, second-first-1) << '\n';
std::cout << s.substr(second+2) << '\n';
}
}
Output:
post
ola tudo bem como esta
alghero.jpg

Answer 3

One option for parsing strings is using regular expressions, for example :
#include <iostream>
#include <regex>
#include <string>
// struct to hold return value of parse function
struct parse_result_t
{
bool parsed{ false };
std::string token1;
std::string token2;
std::string token3;
};
// the parse function
auto parse(const std::string& string)
{
// this is a regex
// ^ match start of line
// (.*)\\\" matches any character until a \" (escaped ") and then escaped again for C++ string
// \w+ match one or more whitepsaces
// (.*)$ match 0 or more characters until end of string
// see it live here : https://regex101.com/r/XnkAZV/1
static std::regex rx{ "^(.*?)\\s+\\\"(.*?)\\\"\\s+(.*)$" };
std::smatch match;
parse_result_t result;
if (std::regex_search(string, match, rx))
{
result.parsed = true;
result.token1 = match[1];
result.token2 = match[2];
result.token3 = match[3];
}
return result;
}
int main()
{
auto result = parse("post \"ola tudo bem como esta\" alghero.jpg");
std::cout << "parse result = " << (result.parsed ? "success" : "failed") << "\n";
std::cout << "token 1 = " << result.token1 << "\n";
std::cout << "token 2 = " << result.token2 << "\n";
std::cout << "token 3 = " << result.token3 << "\n";
return 0;
}

Answer 4

if the strings are always separated by a single space you can just find the first space and last space using std::string::find and std::string::rfind`, split on those characters, and unquote the middle string:
#include <iostream>
#include <tuple>
#include <string>
std::string unquote(const std::string& str) {
if (str.front() != '"' || str.back() != '"') {
return str;
}
return str.substr(1, str.size() - 2);
}
std::tuple < std::string, std::string, std::string> parse_triple_with_quoted_middle(const std::string& str) {
auto iter1 = str.begin() + str.find(' ');
auto iter2 = str.begin() + str.rfind(' ');
auto str1 = std::string(str.begin(),iter1);
auto str2 = std::string(iter1 + 1, iter2);
auto str3 = std::string(iter2 + 1, str.end() );
return { str1, unquote(str2), str3 };
}
int main()
{
std::string test = "post \"ola tudo bem como esta\" alghero.jpg";
auto [str1, str2, str3] = parse_triple_with_quoted_middle(test);
std::cout << str1 << "\n";
std::cout << str2 << "\n";
std::cout << str3 << "\n";
}
You should probably put more input validation into the above, however.

Answer 5

You could use regular expressions for this:
The pattern to search repeatedly for would be: optionally starting with whitespaces \s*; then ([^\"]*) zero or more characters other than quotes (zero or more because you could have several quotes one after the other); and we capture this group (hence the use of parentheses); and finally, whether a quote \" or | the end of the expression $; and we don't capture this group (:?).We use std::regex to store the pattern, wrapping it all within R"()", so that we can write the raw expression.
The while loop does a few things: it searches the next match with regex_search, extracts the captured group, and updates the input line, so that the next search will start where the current one finished.matches is an array whose first element, matches[0], is the part of line matching the whole pattern, and the next elements correspond to the pattern's captured groups.
[Demo]
#include <iostream> // cout
#include <regex> // regex_search, smatch
int main() {
std::string line{"post \"ola tudo bem como esta\" alghero.jpg"};
std::regex pattern{R"(\s*([^\"]*)(:?\"|$))"};
std::smatch matches{};
while (std::regex_search(line, matches, pattern))
{
std::cout << matches[1] << "\n";
line = matches.suffix();
}
}