CODEWITHSUNDEEP
c++arrayschartype-conversion
Brianna Szvenska
Brianna Szvenska

Reputation: 43

Direct converting a const char* text passed through a function into a vector of chars

Imagine that MyTextClass is a custom class that in this case would hold the passed const char "Hello stackoverflowers" into a std::vector<char>:

class MyTextClass{
    private:
        std::vector<char> storage;
    public:
        MyTextClass(const char* _passedchars) //constructor
}

With something like the code above, I want to initialize an instance of MyTextClass by passing a text to it:

MyTextClass textholder("Hello stackoverflowers");

Or even the following if I overload the = operator within MyTextClass:

MyTextClass textholder = "Hello stackoverflowers";

The problem becomes figuring out what the definition of the MyTextClass constructor should look like. I say that because while there is no problem in the constructor receiving a const char passed directly as text like "Hello stackoverflowers", that is an array an thus its length:

1) can't be devised in advance (because it's a passed text of unknown length);

2) nor figured out within the constructor (because sizeof(_passedchars)/sizeof(_passedchars[0]) will only assess the the size of the pointer;

3) and also not retrieved with std::size or the use of std::begin and std::end, since there is no implementation of those for const char.

And without such informations, I just can't figure it out how to convert the const char parameter _passedchars of the constructor of MyTextClass into the internal std::vector<char> that I called storage in the code example above.

Therefore, how could I convert the passed const char into a std:vector<char> within a function, in the case of wanting to create an own char text class?

Upvotes: 1

Views: 177

Answers (2)

M.M
M.M

Reputation: 141628

To use this exact constructor declaration you could write (in the class definition in the header):

MyTextClass(const char* _passedchars)
    : storage( _passedchars, _passedchars + strlen(_passedchars) )
{
}

(note: requires #include <string.h> for strlen).

However the string literal is actually an array. By accepting a pointer you lost the length information which was already available. So you could instead have the constructor as:

template<size_t N>
MyTextClass( const char (&passed)[N] )
    : storage( passed, passed + N - 1 )
{
}

In the latter case you could use std::begin(passed), std::end(passed) instead.

Upvotes: 0

Stack Exchange Broke The Law
Stack Exchange Broke The Law

Reputation: 58909

You can use strlen to determine the length of a C-style string.

Alternatively, you could change the parameter type to std::string and use its size or length function to get the length of the string.

Upvotes: 1

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