Thread: dynamically defined array size in a function

If I don't typecast I get this error:

Code:

'=' : cannot convert from 'void *' to 'long *'

for this function:

Code:

long *TempValue;
TempValue = (long *)calloc(*n, sizeof(long));

and later when I try putting values in there I get another error message:

Code:

fread' : cannot convert parameter 1 from 'long' to 'void *'

from this call:

Code:

fread(TempValue[i], sizeof(long), 1, ptr);

and I know I put & everywhere I'm not supposed to. I don't understand very well where to and not to put it. I'm still trying to figure it all out.

I'm using a C++ compiler. Running the .c file gives me 62 errors. It compiles almost ok as a .cpp.

To start over, you can't allocate space usefully until you know how much spoace you want to allocate. This means that you can't just allocate at compile time unless you at least know a safe maximum. You may know (A) how many fields, or (B) how big they are without knowing both - or may know (C) neither, each field may be a different length with no known maximum.

(A) You can allocate a pointer table of fixed size, and allocate space for each field as you find it, store the data in it and assign its value to one of the pointers in the table.

(B) You can allocate for several fields, fill them, reallocate for more empties and fill them, etc - then address them as an indexed table of fixed length fields.

(C) You can build a linked list of allocated spaces. Like so, will work, maybe what you are looking for:

Code:

struct _mystruct {
    struct _mystruct* next;
    char data[1];
};
struct _mystruct* first, last;

void store_this ( char* string ) {

    struct _mystruct* temp;

    temp = malloc( sizeof(struct _mystruct) + strlen(string) );
    if (!temp) {
        cry_wolf();
        exit(1);
    }
    strcpy(temp->data,string);
    if (!first) first = temp;
    else last->next = temp;
    last = temp;
}

void print_them ( )
{
    for( last = first; last ; last=last->next )
         printf("%s\n",last->data);
}

This will work because the compiler will not complain that you are overstepping the end of the data array in the struct and since it is at the end you just need to alocate enough space
following to hold the second, third, etc characters and the nul char.

After the list is built, the "last" variable is not needed, you can tell when you hit the tail entry because it has an empty (NULL) "next" ptr.