C++ Linked list creation - passing in an array

Question

I am working on creating a linked list in c++, and I can't figure out how to pass an array as an argument in the constructor, or if thats even legal syntax.

This is the error I get:

CheckTextFile.cpp: In constructor ‘Node::Node(char*, int)’:
CheckTextFile.cpp:19: error: incompatible types in assignment of ‘char*’ to ‘char [0u]’
CheckTextFile.cpp: In constructor ‘Node::Node(char*, int, Node*)’:
CheckTextFile.cpp:24: error: incompatible types in assignment of ‘char*’ to ‘char [0u]’

Here is my code:

class Node{
public:
    int length;
    char data[];
    Node * next;
    Node(char x[], int y){
        data = x;
        length = y;
        next = NULL;
    }
    Node(char x[], int y, Node * z){
        data = x;
        length = y;
        next = z;
    }

};

"I am working on creating a linked list in c++", purely as an academic exercise, one hopes. The world doesn't need another C++ list class! — johnsyweb
– johnsyweb, Commented Feb 7, 2012 at 4:14

Greg Hewgill · Accepted Answer · 2012-02-07 04:11:22Z

3

Your argument passing is fine. However, your:

char data[];

declares an array with no size, so it's not surprising that the compiler refuses to generate code to put anything in there. Perhaps try:

std::string data;

This is assuming that your x[] represents a NUL-terminated C string.

After you do that, learn about the member initialisation syntax for constructors.

answered Feb 7, 2012 at 4:11

Greg Hewgill

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2 Comments

user406009 Over a year ago

That's not what the compiler is choking on(I am fairly sure the zero size array is a gcc extension). The compiler is failing on the assignement of the arrays(you can't copy arrays like that in C++).

Alok Save Over a year ago

The error is about assignment inside the constructor not due to passing of pointer to array.

Alok Save · Accepted Answer · 2012-02-07 04:19:20Z

1

You are passing an pointer to the first element of the array, and actually that is correct.

The compiler is complaining about assignment inside the constructor:

data = x;

You cannot assign arrays as such, not like objects, you will have to copy each element from the source array to the target array.
Either using a looping construct or using std::copy.

A trivial way(efficient would be to use std::copy) of doing so:

Node(char x[], int y)
{
     for(int i = 0;i<y; ++i)
     { 
         data[i] = x[i];
     }
     length = y;
     next = 0;
}

Or Simply

std::copy(x,x+y,data);

And it will compile cleanly.

On a side note, you are much better off using std::string rather than using char arrays.

edited Feb 7, 2012 at 4:19

answered Feb 7, 2012 at 4:14

Alok Save

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1 Comment

user406009 Over a year ago

memcpy would probably be the most "C-like" way.

dicaprio · Accepted Answer · 2012-02-07 04:16:29Z

0

First of all, in C++, you can't have an array of unspecified size. Also, you can use a pointer instead of an array or std:string.

answered Feb 7, 2012 at 4:16

dicaprio

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Comments

Rohit Vipin Mathews · Accepted Answer · 2012-02-07 04:54:27Z

0

class Node{
public:
    int length;
    char *ptr_data;  //pointer 
    Node * next;
    Node(char *x, int y){
        ptr_data = x;  //pointer assignment
        length = y;
        next = NULL;
    }
    Node(char *x, int y, Node * z){
        ptr_data = x;    //pointer assignment
        length = y;
        next = z;
    }
};

answered Feb 7, 2012 at 4:54

Rohit Vipin Mathews

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1 Comment

Rohit Vipin Mathews Over a year ago

this will be more efficient as it avoids unnecessary copies. only problem arises if char *x goes out of scope. if such situation exists then you should use copy. and this being char array strcpy(dest,source) will do.

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