How do you append an item into an array using c?

Answer 1

It is possible, if it is a dynamically allocated array:

int n= 0; Elem *p= NULL;

...

AddElem (Elem newval)

{

n += 1; p = (Elem *)realloc (p, n*sizeof (Elem));

p[n-1] = newval;

}

Answer 2

To append an element to an array you must reallocate the array with one more element than it currently has. Reallocation may expand the existing memory, or it may allocate fresh memory if there isn't room for expansion. If new memory is allocated, the existing elements will be copied automatically to the new location. Either way, you will have an empty element at the end of the array which will accommodate the new object.

Note that you cannot expand a static array -- the array must be allocated dynamically to begin with.

The example shown below demonstrates allocation and reallocation of a dynamic array. The code includes fail-safes should any allocation fail.

#include <iostream>

using namespace std;

int main()

{int max=25, i;

char *c, *o;

// Allocate memory for max char types.

if((c=(char*)malloc(max*sizeof(char)))==NULL) return(1); // Report error to caller.

// Initialise memory with consecutive letters (a to y).

for(i=0; i<max; ++i ) c[i]='a'+i;

// Print array.

for(i=0; i<max; ++i) cout<<c[i];

cout<<endl;

// Save current pointer in case of error.

o=c;

// Reallocate the memory to accommodate a new char.

if((c=(char*)realloc(c,++max*sizeof(char)))==NULL)

{ free(o); // Release original pointer.

return(1); // Return error to caller. }

// Insert new char at end of array.

c[max-1]='z';

// Print new array.

for(i=0; i<max; ++i) cout<<c[i]; cout<<endl;

// Release array.

free(c);

return(0); // Report success to caller.

}

Output:

abcdefghijklmnopqrstuvwxy

abcdefghijklmnopqrstuvwxyz