Less White Less White - 7 months ago 32
C++ Question

Replace a loop with strtok by using Standard Library

I have a problem that strtok solves (split substrings from a string) but I
realize that strtok is not safe. I want to use some more modern parts of the C++ standard library.

What should I use instead?

static int ParseLine(std::string line,
std::string seps,
int startIdx,
std::vector<CNode>& collection)
{
if (startIdx > collection.size())
{
throw std::invalid_argument("the start index is out of range");
}
char buf[2000];
strcpy_s(buf, line.c_str());
auto idx = startIdx;
for (auto objectType = strtok(buf, seps.c_str()); objectType != nullptr; idx++)
{
if (idx == collection.size())
{
collection.push_back(CNode(idx));
}
collection[idx].SetObjectType(objectType);
objectType = strtok(nullptr, seps.c_str());
}
return (idx - 1);
}


Here a complete sample that compiles with
_CRT_SECURE_NO_WARNINGS:

#include <string>
#include <vector>
#include <iostream>

class CObject
{
std::string _objectType;

public:
CObject() : _objectType("n/a") {}
void SetObjectType(std::string objectType) { _objectType = objectType; }
std::string GetObjectType() const { return _objectType; }

};

class CNode
{
int _id;
CObject _object;

public:
explicit CNode(int id) : _id(id) {}
void SetObjectType(std::string objectType) { _object.SetObjectType(objectType); }
std::string GetObjectType() const { return _object.GetObjectType(); }

};

// Update the collection of nodes with the object types found in the line specified.
// Return the number of elements in the collection.
static int ParseLine(std::string line, std::string seps, int startIdx, std::vector<CNode>& collection)
{
if (startIdx > collection.size())
{
throw std::invalid_argument("the start index is out of range");
}
char buf[2000];
strcpy_s(buf, line.c_str());
auto idx = startIdx;
for (auto objectType = strtok(buf, seps.c_str()); objectType != nullptr; idx++)
{
if (idx == collection.size())
{
collection.push_back(CNode(idx));
}
collection[idx].SetObjectType(objectType);
objectType = strtok(nullptr, seps.c_str());
}
return (idx - 1);
}

int main()
{
std::string seps = ".";
// 2 3 4 5 6 7 8 9
std::string line = "abc.def.ghi.klm.nop.qrs.tuv.wxyz";
std::vector<CNode> collection { CNode(0), CNode(1), CNode(2) , CNode(3) , CNode(4) , CNode(5) };
auto startAt = 2;
try
{
auto collection_size = ParseLine(line, seps, startAt, collection);
std::cout << collection_size << std::endl;
for (auto value : collection)
{
std::cout << value.GetObjectType() << std::endl;
}
}
catch (std::invalid_argument& e)
{
std::cout << " out of range exception " << e.what() << std::endl;
}
return 0;
}

Answer Source

Here are two examples of splitting a delimited string.

The first uses std::getline with a string stream, specifying a separator character instead of using the default newline character. Only single-character separators may be used with this technique.

The second example uses the <regex> library, which allows separators of arbitrary length and also gives you more control over how a separator is recognized. Note that the dot character must be escaped in the regex specification, because in the regex language, "." acts as a wildcard.

#include <iostream>
#include <sstream>
#include <vector>
#include <regex>

std::vector<std::string> GetlineSplit(std::string const& line) {
    static const char sep = '.';
    std::istringstream liness{line};
    std::vector<std::string> fields;
    for(std::string field; std::getline(liness, field, sep); ) {
        fields.push_back(field);
    }
    return fields;
}

std::vector<std::string> RegexSplit(std::string const& line) {
    std::regex seps("\\."); // the dot character needs to be escaped in a regex
    std::sregex_token_iterator rit(line.begin(), line.end(), seps, -1);
    return std::vector<std::string>(rit, std::sregex_token_iterator());
}

int main() {
    std::string line = "abc.def.ghi.klm.nop.qrs.tuv.wxyz";

    std::cout << "getline split result:\n";
    auto fields_getline = GetlineSplit(line);
    for(const auto& field : fields_getline) {
        std::cout << field << '\n';
    }

    std::cout << "\nregex split result:\n";
    auto fields_regex = RegexSplit(line);
    for(const auto& field : fields_regex) {
        std::cout << field << '\n';
    }
}