c++ command line with system calls - c++

Question

I'm writing a shell in c++, and I need a constructor for my CommandLine class that parses a command from the istream, and then uses the calloc() and free() system calls to dynamically create argc and argv variables. I don't get how to use the system calls to do this, and no tutorial has helped.

Answer 1

Here's an example very similar to what you're asking for. I found it here: http://www.cplusplus.com/reference/clibrary/cstdlib/calloc
function calloc
void * calloc ( size_t num, size_t size );
Allocate space for array in memory Allocates a block of memory for an
array of num elements, each of them size bytes long, and initializes
all its bits to zero.
The effective result is the allocation of an zero-initialized memory
block of (num * size) bytes.
Parameters
num
Number of elements to be allocated. size
Size of elements.
Return Value A pointer to the memory block allocated by the function.
The type of this pointer is always void*, which can be cast to the
desired type of data pointer in order to be dereferenceable. If the
function failed to allocate the requested block of memory, a NULL
pointer is returned.
Example
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/* calloc example */
#include <stdio.h>
#include <stdlib.h>
int main ()
{
int i,n;
int * pData;
printf ("Amount of numbers to be entered: ");
scanf ("%d",&i);
pData = (int*) calloc (i,sizeof(int));
if (pData==NULL) exit (1);
for (n=0;n<i;n++)
{
printf ("Enter number #%d: ",n);
scanf ("%d",&pData[n]);
}
printf ("You have entered: ");
for (n=0;n<i;n++) printf ("%d ",pData[n]);
free (pData);
return 0;
}