Copy pointer to pointer

Hello!

I would like to put the data in "char * memblock" into "char array[1024]".
Both are pointers so i dont understand why i cannot do that.
I tried to dereference them too but didnt work either.

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{

  ifstream::pos_type size;
  char * memblock;
  char array[1024] = {0};
  ifstream file ("1.txt", ios::in|ios::binary|ios::ate);

   if (file.is_open()){

      size = file.tellg();
      memblock = new char [size];
      file.seekg (0, ios::beg);
      file.read (memblock, size);
      file.close();

      cout  << "the complete file content is in memory \n" << memblock << endl;
      array << memblock;  // ???
      cout  << array;
      delete[] memblock;

   }

}

Try

Code:

strcpy(array, memblock);

array is not a pointer, it is an array. If you want to copy C-style strings, you should use strcpy.

What you want to do can be simplified to:

Code:

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
    ifstream file("compchess.txt", ios::in|ios::binary);

    if (file.is_open()) {
        stringstream ss;
        ss << file.rdbuf();
        string data(ss.str());

        cout << "the complete file content is in memory \n" << data << endl;
    }
}

though the above is not the most efficient method.

Ah yes of course i forgot that we need to use functions to copy pointers.

Thank you Yarin, Tabstop and Laserlight!

Err Tabstop, i thought that arrays were pointers...

Laserlight your solution looks simpler, thanks, but i cant seem to use strcpy(array, data) with it:

Code:

int main()
{
    ifstream file("1.txt", ios::in|ios::binary);

    if (file.is_open()) {
        stringstream ss;
        char array[1024] = {0};
        ss << file.rdbuf();
        string data(ss.str());
        strcpy(array, data);

        cout << "\n" << array << endl;
    }
}

The point is to avoid the use of a fixed size array of char by using a std::string. If you do want to use a fixed size array of char, then dynamic memory allocation is unnecessary, since no matter how many characters you read, you cannot fit more than 1024 (or 1023 if this is to be a null terminated string) characters into an array of 1024 characters.

Ok, i see.

Thank you for the explanation!

Have a good day!

Originally Posted by Ducky

Err Tabstop, i thought that arrays were pointers...

Nope. In certain contexts, the name of an array can be used as though it were a pointer (for instance in passing to a function, an array will be treated as a pointer to the first element).

Originally Posted by Ducky

Laserlight your solution looks simpler, thanks, but i cant seem to use strcpy(array, data) with it:

Code:

int main()
{
    ifstream file("1.txt", ios::in|ios::binary);

    if (file.is_open()) {
        stringstream ss;
        char array[1024] = {0};
        ss << file.rdbuf();
        string data(ss.str());
        strcpy(array, data);

        cout << "\n" << array << endl;
    }
}

I think you need to decide whether you're writing C++ (string) or C (strcpy, char[]).

Originally Posted by tabstop

I think you need to decide whether you're writing C++ (string) or C (strcpy, char[]).

Can we replace a 'char buffer[]' with a 'string buffer'?

Because i use the recv() function that takes a char* buffer as argument and when i
try to replace it with 'string buffer' or 'string* buffer' the compiler doesn't like it.

Thanks!

Originally Posted by Ducky

Can we replace a 'char buffer[]' with a 'string buffer'?

It depends on the situation.

Originally Posted by Ducky

Because i use the recv() function that takes a char* buffer as argument and when i
try to replace it with 'string buffer' or 'string* buffer' the compiler doesn't like it.

There is no implicit conversion from std::string to char*. You can perform such a conversion for a std::string named s by writing &s[0], but at the moment the internal buffer of a std::string is not guaranteed to be contiguous, so to be absolutely safe you should use a std::vector<char> instead (or just use an array of char, or a std::tr1::array<char, N>).

Thats sounds more complicated (taking up more lines) than just using char buffer[].