storing and displaying char in vectors

[avillageofbigheads]

As part of learning c++, rather than using std::string, i want to use char to store and display words. so I wrote a simple program.

    int max = 10;
    std::vector<char> vec;
    
    for(int i=0;i<3;i++){
      
      char ch[max];
      std::cout<<"Enter your favorite color:";
      std::cin.getline(ch,max);
         
      vec.push_back(ch[max]);  
      std::cout<< ch <<"\n";
      std::cout<< vec[i] <<"\n";
      
    }

I am able to get the user input data and display it, but seem to have problem with storing the data in a vector and displaying the vector data within the same FOR loop. Rather than use iterators to display the vector data in a different FOR loop, i wanted to see if I could display the data within the same loop.


From what I read online, i have a feeling this might not be working due to std::vector<char> vec being neither assignable or copyable. Is that right ? or if I am mistaken, what is causing this problem and how can i use char to store words in a vector and display them within the same FOR loop?

[gunnerfunner]

std::vector<char> stores char's i.e. each element is a single char – I suspect the favorite colors each run to more one char?

part of learning c++, rather than using std::string

why? Wouldn't you learn c++ best practices as it were?

[avillageofbigheads]

@gunnerfunner I understand the best practices idea. but i don't think it is impossible to use char and store data. I just want to be able to accomplish this. This will help me understand the limitations of each concept. and helps me understand the 'whys' about each command.

[coder777]

From what I read online, i have a feeling this might not be working due to std::vector<char> vec being neither assignable or copyable. Is that right ?

That's wrong. It is actually both and also moveable.

What you're doing wrong is on line 10 using max as an index.

I don't see the use of a vector in this example...

[avillageofbigheads]

@coder777 I want to implement a program using char,vector and 'words' (rather than individual letters).

My basic premise: The user is prompted for a word. The word is input into a char variable and stored in a vector.

I set out on this idea. If you think my example of a program is wrong. Could you help me come up with a simple program where I can implement all the three concepts.

If you think I'm being adamant, I hope you'll see that I'm doing this just to understand limitations of concepts and ideas.

[gunnerfunner]

 to std::vector<char> vec being neither assignable or copyable. Is that right ? or if I am mistaken, what is causing this problem

it's C-style arrays that are not copyable and assignable, so if you really want to use them try something on the following lines:

#include <iostream>
#include <vector>

constexpr auto MAX = 10;

struct charNames
{
    char ch[MAX];
    charNames()
    {
        std::cout << "Enter favorite color \n";
        //size restrictions apply
        std::cin.getline(ch, MAX);
    }
};
std::ostream& operator << (std::ostream& os, const charNames& c)
{
    os << c.ch << "\n";
}

int main()
{
    std::vector<charNames> names{};

    for (size_t i = 0; i < 3; ++i)
    {
        names.emplace_back(charNames());
    }
    for (const auto& elem : names)std::cout << elem;
}

this is for learning but in actual programs prefer std::string

[avillageofbigheads]

@gunnerfunner

I've done the program with std::string. I got curious with the char option. i believe to get to where you are, I need to try different ways of implementing stuff rather do stuff just one way. Hence this idea.

And thank you for approach. This is closer to what I wanted to do. I just have to rack my brains to come up with different ideas to learn more.

[JLBorges]

> As part of learning c++, rather than using std::string ...

The stream extraction operator (deliberately) does not use an auxiliary std::string;
there should be a few things to learn from studying it.

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

std::vector<char> make_vec_str( const char* cstr )
{
    if(cstr)
    {
        const char* end = cstr ;
        while( *end++ ) ;
        return { cstr, end } ;
    }

    else return {} ;
}

std::istream& operator >> ( std::istream& stm, std::vector<char>& vec_str )
{
    vec_str.clear() ;

    const auto& ctype = std::use_facet< std::ctype<char> > ( stm.getloc() ) ;
    char c ;

    // extract and discard leading white space
    while( std::char_traits<char>::not_eof( stm.peek() ) &&
           ctype.is( std::ctype_base::space, stm.peek() ) ) stm.get(c) ;

    // append characters till the first white space character
    while( stm.get(c) && !ctype.is( std::ctype_base::space, c ) ) vec_str.push_back(c) ;

    // put back the last white space extracted (if any)
    if( !vec_str.empty() ) stm.putback(c) ;

    return stm ;
}

// TO DO: getline

std::ostream& operator << ( std::ostream& stm, const std::vector<char>& vec_str )
{
    for( char c : vec_str ) stm << c ;
    return stm ;
}

int stoi( const std::vector<char>& vec_str, std::size_t* pos = 0, int base = 10 )
{ return std::stoi( std::string{ std::begin(vec_str), std::end(vec_str) }, pos, base ) ; }

// TO Do: other string operations

int main()
{
    std::vector<char> first, second, third ;

    std::cin >> first >> second >> third ;

    std::cout << " first: " << first << '\n'
              << "second: " << second << '\n'
              << " third: " << third << '\n' ;

    if( first == second ) std::cout << "first == second\n" ;
    if( second > third ) std::cout << "second > third\n" ;

    const std::vector<char> vec_str = make_vec_str( "123456" ) ;
    std::cout << stoi(vec_str) + 7'000'000 << '\n' ;
}

http://coliru.stacked-crooked.com/a/460b00c3a206baaf

[coder777]

To organize words just with vectors you may use vector of vectors:

    int max = 10;
    std::vector<std::vector<char> > vec; // The inner vector is the word.
    
    for(int i=0;i<3;i++){
      
      vec.emplace_back(max); // This creates an instance of the inner vector with 'max' char
      std::cout<<"Enter your favorite color:";
      std::cin.getline(vec.back().data(),max); // This gets the data of the previously created vector
         
      vec.push_back(ch[max]);  // This is not needed
      std::cout<< ch <<"\n";
      std::cout<< vec[i].data() <<"\n"; // Accessing the data of the inner vector which contains the c-string
      
    }

[avillageofbigheads]

@JLBorges This sure is a lot to process. But this is wanted. To study different approaches to get me to understand concepts better. Thank you,


@coder777 Here is something I learnt today. The benefits of using vectors/struct within vectors . Thank you .