caloc errors in compile

[Dameon99]

Hi, when i try to compile my code it comes up with two errors both in the same function.

The errors are both the same:

106assig-4.cpp invalid conversion from `void*' to `int**'

Here is my code:

int **setMem(int **matrixPointer, int rows, int columns)
{
    // Allocate memory for each row.
    matrixPointer = calloc(rows, sizeof(int *)); //error here!!
 
    // Allocate memory for each columns within each row. 
    for (int index1 = INIT; index1 < rows; index1++)
    {
                                // error on line below 
        matrixPointer[index1] = calloc(columns, sizeof(int));
    }
 
    return matrixPointer;
}
 

matrixPointer is an array of arrays using double pointers (or 2D array). rows are the first arrays size and columns is the second. It is an integer array. the module is supposed to assign memory to my array using the pointer.

PLease could some one let me know how I can fix this!? I will provide the rest of my code if necessary. Please request any details required.

[JosAH]

If you're compiling this as C everything should be fine as long as you've included
the <stdlibh> header file. If you're compiling this as C++ code you also have to
explicitly cast the return value of the calloc() function.

kind regards,

Jos

[Dameon99]

Ive got
#include <stdlb.h>

its only C not C++.. still wont compile..

[Dameon99]

syntax correction:

#include <stdlib.h>

[Dameon99]

how would you write the above lines in error for the same purpose?

Ive looked through books and manuals galore for the last few hours and ive found nothing wrong with my code.

[sicarie]

Could you post the errors you are getting?

[Dameon99]

Could you post the errors you are getting?

they are posted above:

invalid conversion from void* to int**

thats all the information it gives me and that is for both sections I have marked in the above code.

any help is hugely appreciated.. im entirely stumped.. and ill admit a bit frustrated with the language. Im using the Bloodshed Dev-C++ compiler that was recommended to me on this forum if that is any help.

[weaknessforcats]

matrixPointer = calloc(rows, sizeof(int *)); //error here!!

The error is that calloc is returning the addess of an int (int*) and matrixPointer is the address of an int pointer (int**). The compiler is producing the error because it knows that to allow the assignment will result in pointer aritmetic errors.

What you mean to say is:

 *matrixPointer = calloc(rows * sizeof(int)); 
 

[Dameon99]

The error is that calloc is returning the addess of an int (int*) and matrixPointer is the address of an int pointer (int**). The compiler is producing the error because it knows that to allow the assignment will result in pointer aritmetic errors.

What you mean to say is:

 *matrixPointer = calloc(rows * sizeof(int)); 
 

Thanks, I feel that I am getting closer to a solution. I copied and pasted this into my code but still no banana. it wouldnt compile saying that there was too many arguments for calloc. could you please put fill in a bit more on the syntax and Ill try it again? are there supposed to be commas somewhere in the calloc parametres (like: "*matrixPointer = calloc(rows, * sizeof(int));")?

my code as it stands now is:

int **setMem(int **matrixPointer, int rows, int columns)
{
    // Allocate memory for each row.
    *matrixPointer = calloc(rows, sizeof(int));
 
    // Allocate memory for each columns within each row. 
    for (int index1 = INIT; index1 < rows; index1++)
    {
        *matrixPointer[index1] = calloc(columns, sizeof(int));
    }
 
    return matrixPointer;
}
 

[Dameon99]

im still trudging away with the code.. after the changes now I am getting a very similar message for the same code sections.

invalid conversion from void* to int*

I still dont understand..

[Banfa]

 *matrixPointer = calloc(rows * sizeof(int)); 
 

No he had it right originally wfc, note it is calloc NOT malloc and calloc takes 2 parameters, the number of items in the array and the size of each item.

Dameon99

You say you are using Dev-C++ are you absolutely sure you are not compiling for C++ because that would definitely produce the errors you are getting. Are you sure your file extension is .c, are you sure that there are no command line switches in use that are forcing compilation as C++ even though the file has a c extension (some compilers have switches for this). Are you sure that Dev-C++ is capable of compiling C (as opposed to C++).

It may be time to check your compiler documentation (if you have already done that of course).

[Dameon99]

Problem Fixed!!!!!

For some reason I had to typecast calloc to an int. I think it may have been compiling as a C++ file :-S. I just read in a guide on the net that you should always typecast it even in C.

Solution was (for those who are curious):

    *matrixPointer = (int *)calloc(rows, sizeof(int *));
 

and

    *matrixPointer[index1] = (int)calloc(columns, sizeof(int));
 

Thanks so much for everyones help :-D. Much appreciated.

[JosAH]

Casting the return value of calloc (a void*) to an int is dead wrong. Reread my
reply #2; the answer is already there.

kind regards,

Jos