How to realloc() memory to string array

Question

I have a string array of,

char *string_arr[] = {     "Hi",  "Hi2", "Hi3", "Hi4"    };

Now I need to realloc memory to the array, because I have to insert another element into the array like "Hi5". How can I do that?

I tried:

string_arr = realloc (.....);

but it doesn't work, it gives: "incompatible types in assignment" error.

sizeof (string_arr[0]); doesnt give the right space. other elements are 3 seen chars but zeroth element is 2 seen chars — huseyin tugrul buyukisik
– huseyin tugrul buyukisik, Commented Jul 18, 2012 at 17:43

paulsm4 · Accepted Answer · 2012-07-18 17:38:42Z

4

You can only "realloc()" a pointer to memory you got from "malloc ()".

char **string_arr;

int nelms = 10;
string_array = (char **)malloc (sizeof (char *) * nelms);
if (!string_array) {
  perror ("malloc failed");
  return;
}

string_array[0] = strdup ("Hi");
string_array[1] = strdup ("Hi2");
string_array[2] = strdup ("Hi3");
string_array[3] = strdup ( "Hi4");
...
string_array = realloc (...);
...

answered Jul 18, 2012 at 17:38

paulsm4

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2 Comments

P.P Over a year ago

...or previously returned by a calloc() or realloc().

t0mm13b Over a year ago

Hummm... the last line of the code sample above, what happens if realloc fails, you've got a memory leak there on string_array...

chmeee · Accepted Answer · 2012-07-18 17:41:41Z

3

There are two problems with your code:

1) You are attempting to realloc() a fixed-size array. realloc() can only be used on memory allocated using malloc().

2) string_arr is an array, not a pointer. Arrays do degenerate into pointers when used as rvalues in expressions, but are still distinct data types as lvalues.

answered Jul 18, 2012 at 17:41

chmeee

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Comments

Oliver Charlesworth · Accepted Answer · 2012-07-18 17:39:04Z

3

You cannot realloc an array that has not been malloc-ed.

answered Jul 18, 2012 at 17:39

Oliver Charlesworth

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Comments

Jeyaram · Accepted Answer · 2012-07-18 18:04:58Z

2

Memory for the string array will be allocated in read-only section.

      .section        .rodata
    .LC0:
            .string "Hi"
    .LC1:
            .string "Hi2"
    .LC2:
            .string "Hi3"
    .LC3:
            .string "Hi4"
            .text
    .globl main
            .type   main, @function
    main:
            pushl   %ebp
            movl    %esp, %ebp
            subl    $16, %esp
            movl    $.LC0, -16(%ebp)
            movl    $.LC1, -12(%ebp)
.....
.....

Not in the heap. so you can't use realloc() to extend the memory.

answered Jul 18, 2012 at 18:04

Jeyaram

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Comments

Francis P · Accepted Answer · 2012-07-18 17:40:06Z

0

Create a new array of size +1, transfer the elements from the initial array to the new array.

answered Jul 18, 2012 at 17:40

Francis P

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