invalid conversion from 'char' to 'char*'

[activecat]

Dear guru,

The simplified code below works correctly.
But when I try to replace line 43 with out2[i] = sentence[i];, it gives this compilation error:

invalid conversion from 'char' to 'char*'

Why and how to make it work?

#include <iostream>
#include <cstring>
#include <vector>
using namespace std;


typedef std::vector <void *> gr_vector_void_star;
gr_vector_void_star  output_items;

const char* sentence("Angel");
unsigned int counter(0);

int noutput_items = 5;

int main()
{
    cout << "sentence is '" << sentence << "'" << endl;

    // initialize output_items[0]
    float *temp1[ noutput_items ];
    output_items.push_back( temp1 );

    // store values into output_items[0]
    float *out1 = (float *) output_items[0];
    for (int i=0; i < noutput_items; i++)
     { out1[i] = i * 1.1; }

    // retrieve values from output_items[0]
    float *display1 = (float *) output_items[0];
    for (int i=0; i < noutput_items; i++)
     { cout << display1[i] << endl; }

    cout << endl;

    // initialize output_items[1]
    char* *temp2[ noutput_items ];
    output_items.push_back( temp2 );

    // store values into output_items[1]
    char* *out2 = (char**) output_items[1];
    for (int i=0; i < noutput_items; i++)
     {
        out2[i] = "k";     // this works!
        // out2[i] = sentence[i];          // error: invalid conversion from 'char' to 'char*' [-fpermissive]
        // out2[i] = (char) sentence[i];   // error: invalid conversion from 'char' to 'char*' [-fpermissive]
        // out2[i] = (char*) sentence[i];  // error: segmentation fault
     }

    // retrieve values from output_items[1]
    char* *display2 = (char**) output_items[1];
    for (int i=0; i < noutput_items; i++)
     { cout << display2[i] << endl; }

    return 0;
}

Output of the above code:

sentence is 'Angel'
0
1.1
2.2
3.3
4.4

k
k
k
k
k

Process returned 0 (0x0)   execution time : 0.002 s
Press ENTER to continue.

Note:
The objective is to be able to retrieve the characters out from output_items[1] later, as below.

    anytype display2 = (anytype) output_items[1];
    for (int i=0; i < noutput_items; i++)
     { cout << display2[i] << endl; }

Desirable output:

A
n
g
e
l

The requirement is that, output_items must be defined as a vector of void pointers.
temp2, out2, sentence and display2 may be declared differently as needed.

How to do it?
Please advise, thanks.
activecat

[MikeyBoy]

sentence is an array of chars, so sentence[i] has type char.

out2 is an array of pointers to char, so out2[i] has type char*.

So it should now be obvious why you're getting that message.

If each element of out2 is intended to be a single character, then why not make it an array of chars?

[z05DSL3A]

const char* sentence : This is a pointer to a constant char
char* *out2 : This is a pointer to a pointer to a char

They are not arrays.

[activecat]

@ MikeyBoy,

Thanks. I forget to mention that the requirement is to correctly cast out2 from output_items[1], which is a void pointers.

[activecat]

@ Canis lupus:
I think you are right, both sentence and out2 are not arrays.
In this case how to define temp2, out2, sentence and display2 accordingly to make the program works ?

Note:
The objective is to be able to retrieve the characters out from output_items[1] later, for example, as follows.

    anytype display2 = (anytype) output_items[1];
    for (int i=0; i < noutput_items; i++)
     { cout << display2[i] << endl; }

Expected output:

A
n
g
e
l

[MikeyBoy]

So let me get this right - output_items is an array of pointers. What do those pointers point to? Single characters? The first character each of several character arrays?

[activecat]

@MikeyBoy:
output_items is a vector of void pointers. Hence both output_items[0] and output_items[1] are void pointers.
output_items[0] points to an array of float numbers.
output_items[1] can point to anything as long as our objective is achieved.

typedef std::vector <void *> gr_vector_void_star;
gr_vector_void_star  output_items;

[activecat]

Dear all above,

I have create another thread, putting this question into a simpler way.
Refer http://www.cplusplus.com/forum/general/121976/

Let's meet there, thank a lot.