how to pass arrays as parameters in constructor? c++

Question

I am trying to make a constructor for class call, in which 4 arrays are passed as parameters. I've tried using *,&, and the array itself; however when I assign the values in the parameters to the variables in the class, I get this error :

 call.cpp: In constructor ‘call::call(int*, int*, char*, char*)’:
 call.cpp:4:15: error: incompatible types in assignment of ‘int*’ to ‘int [8]’
 call.cpp:5:16: error: incompatible types in assignment of ‘int*’ to ‘int [8]’
 call.cpp:6:16: error: incompatible types in assignment of ‘char*’ to ‘char [14]’
 call.cpp:7:16: error: incompatible types in assignment of ‘char*’ to ‘char [14]’

I would appreciate your help in finding my error and helping me correct it. here is my code:

.h file

#ifndef call_h
#define call_h
class call{
private:
    int FROMNU[8]; 
    int DESTNUM[8];
    char INITIME[14]; 
    char ENDTIME[14];

public:
    call(int *,int *,char *,char *);
};
#endif

.cpp file

call:: call(int FROMNU[8],int DESTNUM[8],char INITIME[14],char ENDTIME[14]){
    this->FROMNU=FROMNU;
    this->DESTNUM=DESTNUM;
    this->INITIME=INITIME;
    this->ENDTIME=ENDTIME;
}

Replace the arrays by std::array or std::tr1::array if you don't have C++11 support (or altenratively, boost::array) — juanchopanza
– juanchopanza, Commented Feb 18, 2013 at 0:52
Arrays are not the same thing as pointers, although in many cases they are demoted to pointers. For your use case, consider std::array instead of [] arrays. — us2012
– us2012, Commented Feb 18, 2013 at 0:52

Cheers and hth. - Alf · Accepted Answer · 2013-02-18 01:04:57Z

4

Raw arrays are non-assignable and generally difficult to handle. But you can put an array inside a struct, and assign or initialize that. Essentially that's what std::array is.

E.g. you can do

typedef std::array<int, 8>   num_t;
typedef std::array<char, 14> time_t;

class call_t
{
private:
    num_t    from_;
    num_t    dest_;
    time_t   init_;
    time_t   end_;

public:
    call_t(
        num_t const&     from,
        num_t const&     dest,
        time_t const&    init,
        time_t const&    end
        )
        : from_t( from ), dest_( dest ), init_( init ), end_( end )
    {}
};

But this still lacks some essential abstraction, so it's merely a technical solution.

To improve things, consider what e.g. num_t really is. Is it, perhaps, a telephone number? Then model it as such.

Consider also using standard library containers std::vector and, for the arrays of char, std::string.

edited Feb 18, 2013 at 1:04

answered Feb 18, 2013 at 0:58

Cheers and hth. - Alf

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Comments

xmllmx · Accepted Answer · 2013-02-18 01:13:57Z

1

Passing a raw array as an argument is possible in C++.

Consider the following code:

template<size_t array_size>
void f(char (&a)[array_size])
{
    size_t size_of_a = sizeof(a); // size_of_a is 8
}

int main()
{
    char a[8];
    f(a);
}

edited Feb 18, 2013 at 1:13

answered Feb 18, 2013 at 1:06

xmllmx

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2 Comments

us2012 Over a year ago

You're using C++11's auto in your code sample. Who in their right mind would have access to C++11 and use that instead of std::array?

xmllmx Over a year ago

'auto' is not essential here. I replaced it with explicit 'size_t'

Karthik T · Accepted Answer · 2013-02-18 00:58:47Z

0

In C/C++ you cannot assign arrays by doing this->FROMNU=FROMNU; thus your method wont work, and is one half of your error.

The other half is that you try to assign a pointer to the array. Even if you pass arrays to a function, they decay to pointers to the first element, despite what you say in the definition.

answered Feb 18, 2013 at 0:58

Karthik T

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