CODEWITHSUNDEEP
cdynamic-arraysrealloc
Fábio Soldá
Fábio Soldá

Reputation: 19

Increase numbers of elements in array of strings in C

I'm beginner in the studies of C language (not C++) and I'm trying to define a dynamic array of strings, but I'm experiencing difficulties for appending an element.

I have tried to define the array as:

char **e = malloc(3 * sizeof(char *));
e[0] = "abc";
e[1] = "def";
e[2] = "ghi";

It ran successfully, but trying to resize it, using:

  **e = realloc(e, 4 * sizeof(char *));

Returned the error: "assignment makes integer from pointer without a cast". What am I doing wrong?

Thanks, Fábio

Upvotes: 0

Views: 239

Answers (2)

nalzok
nalzok

Reputation: 16117

This is the refined code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
        char **e = malloc(3 * sizeof(char *));
        e[0] = malloc(4 * sizeof(char));
        e[1] = malloc(4 * sizeof(char));
        e[2] = malloc(4 * sizeof(char));
        strcpy(e[0], "abc");
        strcpy(e[1], "def");
        strcpy(e[2], "ghi");
        puts(e[0]);
        puts(e[1]);
        puts(e[2]);
}

Some problems found in your code:

  1. To allocate memory to a pointer, write ptr = malloc(1), not malloc(ptr, 1).

  2. e is a "pointer to pointer to char", while e[0] to e[2] are "pointers to char". So when mallocing e, use sizeof (char *), and when mallocing e[x]', usesizeof (char)` instead.

  3. *e = "abc"; only copy the address of the string literal, not the value it contains. To copy the whole char array, you have to write strcpy(e[0], "abc");.

Upvotes: 0

George
George

Reputation: 2594

Short answer:

e = realloc(e, 4 * sizeof(char *));

Long answer:

Let's split your original declaration char **e = malloc(3 * sizeof(char *)); into declaration and assignment.

char **e;
e = malloc(3 * sizeof(char *));

The first line introduces the variable e and specifies its type char **. The second line assigns the expression that you put on the right side of the = sign to the newly declared variable.

To assign a new value to e, you modify the second line to read:

e = realloc(e, 4 * sizeof(char *));

Upvotes: 2

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