C++ – Convert char** (c) of unknown length to vector (c++)

arrayscc-stringsstringvector

How would one go about converting a C char** to a C++ vector? Is there some built-in functionality one can utilize to do this, or is it better to accomplish it through a series of iterative steps?

EDIT: For various reasons, the number of elements in the C array is unknown. It is possible I could pass that as another parameter, but is that absolutely necessary?

Best Answer

You can simply use the constructor of std::vector that takes two iterators:

const char* arr[] = {"Hello", "Friend", "Monkey", "Face"};
std::vector<std::string> v(std::begin(arr), std::end(arr));

Or if you really have a const char**:

const char** p = arr;
std::vector<std::string> v(p, p + 4);

Which will also work with directly using arr instead of p due to array-to-pointer conversion.

Related Solutions

C# – the difference between String and string in C#

string is an alias in C# for System.String.
So technically, there is no difference. It's like int vs. System.Int32.

As far as guidelines, it's generally recommended to use string any time you're referring to an object.

e.g.

string place = "world";

Likewise, I think it's generally recommended to use String if you need to refer specifically to the class.

e.g.

string greet = String.Format("Hello {0}!", place);

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C++ – How to iterate over the words of a string

I use this to split string by a delimiter. The first puts the results in a pre-constructed vector, the second returns a new vector.

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

template <typename Out>
void split(const std::string &s, char delim, Out result) {
    std::istringstream iss(s);
    std::string item;
    while (std::getline(iss, item, delim)) {
        *result++ = item;
    }
}

std::vector<std::string> split(const std::string &s, char delim) {
    std::vector<std::string> elems;
    split(s, delim, std::back_inserter(elems));
    return elems;
}

Note that this solution does not skip empty tokens, so the following will find 4 items, one of which is empty:

std::vector<std::string> x = split("one:two::three", ':');