CODEWITHSUNDEEP
c++arraysvisual-studiomfc
ANjaNA
ANjaNA

Reputation: 1426

How to create a variable size char array in VC++

const int sizea = 600; 
char sz[sizea];

above code works fine. But below code segment cause errors. I'm working on visual studio 2005 - MFC application

CString strFinal;

.......//strFinal value is dynamically changing . . 

const int size = strFinal.GetLength();
char sz[size];

Error 2 error C2057: expected constant expression
Error 5 error C2070: 'char []': illegal sizeof operand
Error 4 error C2133: 'sz' : unknown size Error 3 error C2466: cannot allocate an array of constant size 0

Upvotes: 6

Views: 24272

Answers (5)

tektok tek
tektok tek

Reputation: 66

I did something like this long time ago the Idea is to work with pointers.

so you need to make structure that has (char and nextPointer) the char represent the current value of the array and the nextPointer represent the next structure of the series

looping all through that pointers u will have your array of whatever you want your structure connected

struct yourStructure {
  Char char;
  double nextPointer;
} ;

so you create first structure and connect to the second and the tree

enter image description here

Upvotes: 0

Samitha
Samitha

Reputation: 21

you can use vector as a dynamic array. Try this.

#include <vector> // use this header
#include <iostream>

using namespace std; // use this namespace

int main()
{
    vector<int> v; //declare dynamic array equivalent

    for (int i = 0; i < 10; ++i) {
        v.push_back(10 + i);
    }

    cout << "vector data: " << endl;
    print_collection(v);

    while (v.begin() != v.end()) { 
        cout << "v.back(): "; print_elem(v.back()); cout << endl;
        v.pop_back();
    }
}

Upvotes: 2

Mike Seymour
Mike Seymour

Reputation: 254631

In the current version of C++, arrays must have a fixed size, specified by a compile-time constant. If you need to use a run-time value, then your options are:

  • most portably, use a dynamic array class such as std::string or std::vector<char>;
  • use a compiler that supports C99 variable-length arrays as a non-standard extension;
  • wait a year for dynamic arrays to (hopefully) be introduced in C++14 (and perhaps wait a bit longer for your compiler vendor to catch up).

Upvotes: 5

mesmerizingr
mesmerizingr

Reputation: 1447

It produces an error because GetLength() returns you an arbitrary value, not statically defined.

The proper way is to allocate enough memory to hold your string and, if required, the NULL-terminated symbol either by calling malloc or by using the new operator (if compiling with C++ compiler).

Upvotes: 0

mark
mark

Reputation: 5469

Normal use-case is to use new (and delete when you're done) for variable-sized elements. If you must use the stack, you can use alloca.

char *psz = new char[size+1];  // +1 you probably want zero-termination
...
delete [] psz;

Upvotes: 2

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