2

Here is my code:

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

using namespace std;

template<int N>
class Arguments
{
protected:
    string arguments[N];
public:
    Arguments(const string(&arg)[N]) : arguments{ arg } {}
    string operator[](const int &i) const { return arguments[i]; }
};

int main()
{
    string arr[3] = { "arg1", "arg2", "arg3" };
    Arguments<3> args(arr);

    cout << args[2];

    return 0;
}

This is the error i get:

Severity    Code    Description Project File    Line    Suppression State
Error   C2440   'initializing': cannot convert from 'const std::string [3]' to 'std::string'    
coursework_draft    C:\dev\coursework_draft\coursework_draft\coursework_draft.cpp   13

What do i need to change?

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2
  • 4
    You can't initialize an array with another array, only elementwise. Either use a loop to copy the elements, or use std::array which can be copied normally. Commented May 19, 2020 at 16:59
  • I fixed it. Thank you! Commented May 19, 2020 at 17:06

3 Answers 3

Reset to default
5

Arrays are not copyable in C++. So this is never going to work

 Arguments(const string(&arg)[N]) : arguments{ arg } {}

You could use std::array<std::string, N> instead, or you could copy the array element by element in the body of the constructor.

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7 Comments

fixed it. Thank you!
Arguments(const string(&arg)[N]) : arguments( arg ) {} seems to work also... what is wrong with it?
@Klaus It's not legal C++. g++ is using a non-standard extension to allow it to compile
@NathanOliver: Compiles also with -pedantic which should warn on such extensions... OK, it is like it is :-) Thanks!
@Klaus Seems like a bug in GCC.
|
1

This:

arguments{ arg }

is list-initialisation and means that the first element of arguments is initialised with arg. But the elements of arguments are std::string, which cannot be initialised with an array of strings.

Arrays are not copy-initialisable.

Classes however can be copy initialisable, and they can have array members. As such, you can use a class as a wrapper around an array that can be conveniently copied. The standard library has a template for such array wrapper. Its name is std::array.

Another option is to copy the array in the constructor body using std::copy or similar function.

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1 Comment

fixied it. Thank you!
0

You can use std::copy:

Arguments(const string(&arg)[N]) {
   std::copy(arg, arg + N, arguments); 
}

Here's a demo.

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3 Comments

i had those. the compiler said to use { } to initialize an array
This might work with g++ but it wont with clang and is not standard
@NathanOliver Oh, I didn't know that. thanks, edited.

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