I am trying to extract the first numbers from each block of numbers from the next string.
string s = "f 1079//2059 1165//2417 1164//2414 1068//1980";
In this example I need to extract 1079, 1165, 1164 and 1068
I have tried with getline and substr but I have not been able to.
You can utilize the <regex>
(C++ regular expression library) with pattern (\\\\d+)//
. Locate the numbers before double slashes. Also using the parentheses to extract the numbers only by submatch.
Here is usage.
string s = "f 1079//2059 1165//2417 1164//2414 1068//1980";
std::regex pattern("(\\d+)//");
auto match_iter = std::sregex_iterator(s.begin(), s.end(), pattern);
auto match_end = std::sregex_iterator();
for (;match_iter != match_end; match_iter++)
{
const std::smatch& m = *match_iter;
std::cout << m[1].str() << std::endl; // sub-match for token in parentheses, the 1079, 1165, ...
// m[0]: whole match, "1079//"
// m[1]: first submatch, "1070"
}
I usually reach for istringstream
for this kind of thing:
std::string input = "f 1079//2059 1165//2417 1164//2414 1068//1980";
std::istringstream is(input);
char f;
if (is >> f)
{
int number, othernumber;
char slash1, slash2;
while (is >> number >> slash1 >> slash2 >> othernumber)
{
// Process 'number'...
}
}
here is an attempt with getline and substring which works.
auto extractValues(const std::string& source)
-> std::vector<std::string>
{
auto target = std::vector<std::string>{};
auto stream = std::stringstream{ source };
auto currentPartOfSource = std::string{};
while (std::getline(stream, currentPartOfSource, ' '))
{
auto partBeforeTheSlashes = std::string{};
auto positionOfSlashes = currentPartOfSource.find("//");
if (positionOfSlashes != std::string::npos)
{
target.push_back(currentPartOfSource.substr(0, positionOfSlashes));
}
}
return target;
}
Or there is another split way to extract tokens, but it may involve some string copy.
Consider a split_by
function like
std::vector<std::string> split_by(const std::string& str, const std::string& delem);
Possible implementations in Split a string in C++?
Make string be splitted by first, then splitted by
//
and extract first item.
std::vector<std::string> tokens = split_by(s, " ");
std::vector<std::string> words;
std::transform(tokens.begin() + 1, tokens.end(), // drop first "f"
std::back_inserter(words),
[](const std::string& s){ return split_by(s, "//")[0]; });
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