Question about memory allocation / reallocation

Question

I just finished the task of allocating memory with the current program that I am writing, but I am not happy with what I needed to do to fix it.

In my program, I created an array of structures, redistributing the space for the array every time I wanted to add a structure to it. Here is a general version of my structure and a function that would add the structure to the array:

typedef struct Example {
    const char* name;
    int (*func)(int, int);
    int bool_switch;
}

int add_struct_to_array( Example **example_array, int *ex_array_size, int name, int (*func)(int, int), int bool_switch)
{
    // first, make a new struct
    Example *new_example = (Example *) calloc( 1, sizeof( Example ) );
    if( new_example != NULL ) {
        new_example->name = name;
        new_example->func = func;
        new_example->bool_switch = bool_switch;
        ( *ex_array_size )++;
    } else {
        printf( "Errror allocating %s\n", name );
        exit( -1 );
    }

    // now, realloc the array of structs and add the new member to it
    Example **temp_example_array = ( Example** )realloc( example_array, ( *ex_array_size ) * sizeof( Example* ) );
    if( temp_example_array != NULL ) {
        example_array = temp_example_array;
        example_array[ ( *ex_array_size ) - 1 ] = new_example;
    } else {
        printf( "Reallocation failed\n" )
        exit( -1 );
    }
    return 0;
}

And here I will call the functions (note how I initially allocate an array of structures because there was a problem)

#include "example_struct.h"

int main( int argc, char **argv )
{
    int ex_array_size = 0;
    Example **example_array = ( Example** )calloc( 0, sizeof( Example* ) );

    add_struct_to_array( example_array, &ex_array_size, "name", &function, 1 );
    ...
    ...
    add_struct_to_array( example_array, &ex_array_size, "other_name", &other_func, 0 );

    /* Do stuff here */

    example_array_free( example_array );

    return 0;
}

, -, , 0 , , . , , error for object 0x100100080: pointer being reallocated was not allocated. example_array 0x100100080, , , 0x100100090, example_array .

, , . , example_array, , . ?

** EDIT **

, . , , pmg crypto. :

/* example_struct.h */
int add_struct_to_array( Example *example_array, int *ex_array_size, int name, int (*func)(int, int), int bool_switch)
{
    Example temp_example_array = realloc( example_array, ( ( *ex_array_size ) + 1 ) * sizeof( Example ) );

    if( temp_example_array != NULL ) {
        example_array = temp_example_array;
        Example new_example;
        new_example.name = name;
        new_example.func = func;
        new_example.bool_switch = bool_switch;
        example_array[ ( *ex_array_size ) ] = new_example;
        ++( *ex_array_size );
    } else {
        fprintf( stderr, "Error reallocating for %s", name );
        exit( -1 );
    }
    return 0;
}



/* main.c */
...
...
#include "example_struct.h"
int main( int argc, char **argv )
{
    int ex_array_size = 0;
    Example *example_array = NULL;

    add_struct_to_array( example_array, &ex_array_size, "name", &func, 1 );
    add_struct_to_array( ... );
    ...
    add_struct_to_array( example_array, &ex_array_size, "other name", &other_func, 0 );

    example_free( example_array );
}

realloc , .

/* main.c */
...
...
#include "example_struct.h"
int main( int argc, char **argv )
{
    int ex_array_size = 0;
    Example *example_array = NULL;

    add_struct_to_array( example_array, &ex_array_size, "name", &func, 1 );
    add_struct_to_array( ... );
    ...
    add_struct_to_array( example_array, &ex_array_size, "other name", &other_func, 0 );


    printf( "%s\n", example_array[0].name ) /* Segfault */


    example_free( example_array );
}

.

Answer 1

( ++ ), , , , ), ideone (http://ideone.com/iMByR)

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

struct protected {
  int this;
  int (*catch)(int, int);
  int friend;
};

int catch(int mutable, int virtual) {
  return mutable + virtual;
}

struct protected *add_one(struct protected **private,
                          int *explicit, int using,
                          int (*catch)(int, int), int friend) {
  struct protected *new;

  new = realloc(*private, (*explicit + 1) * sizeof *new);
  if (new) {
    *private = new;
    (*private)[*explicit].this = using;
    (*private)[*explicit].catch = catch;
    (*private)[*explicit].friend = friend;
    (*explicit)++;
  }
  return new;
}

/* create an array of structs using dynamic memory */
/* keep adding elements to it, and growing it as needed */
int main(void) {
  int using;
  /* explicit contains the number of elements in the try array */
  int explicit = 0;
  struct protected *try = NULL;

  /* create and grow */
  for (using = 0; using < 7; using++) {
    if (add_one(&try, &explicit, using + 1, catch, 0) == NULL) {
      fprintf(stderr, "failure at loop %d\n", using);
      exit(EXIT_FAILURE);
    }
  }

  /* verify */
  for (using = 0; using < explicit; using++) {
    printf("%d: %d\n", using, try[using].this);
  }

  free(try);
  return 0;
}

Answer 2

realloc NULL ... malloc

*p = NULL;
new = realloc(p, 42); /* same as new = malloc(42); */
if (!new) { /* error */ }
p = new;

, calloc ( , ), NULL realloc .

int main(void) {
    Example *example_array = NULL;
    add_struct_to_array(&example_array, &ex_array_size, "name", function, 1);
    /* ... */
    free(example_array);
}

Answer 3

. .

: , pmg Bart van Ingen Schenau

int add_struct_to_array( Example ***example_array, int *ex_array_size, int name, int (*func)(int, int), int bool_switch)
{
     Example **temp_example_array = realloc(*example_array,((*ex_array_size) + 1) * sizeof(Example *) );
     Example *new_example = calloc(1, sizeof( Example ) );

    if( temp_example_array != NULL && new_example != NULL ) {
        *example_array = temp_example_array;
        *example_array[ *ex_array_size ] = new_example;
        new_example->name = name;
        new_example->func = func;
        new_example->bool_switch = bool_switch;
        ( *ex_array_size )++;
    } else {
        printf( "Error allocating %s\n", name );
        exit( -1 );
    }
    return 0;
}


#include "example_struct.h"

int main( int argc, char **argv )
{
    int ex_array_size = 0;
    Example **example_array = calloc( 0, sizeof( Example* ) );

    add_struct_to_array( &example_array, &ex_array_size, "name", &function, 1 );
    ...

    add_struct_to_array( &example_array, &ex_array_size, "other_name", &other_func, 0 );

    ...

    example_array_free( example_array );

    return 0;
}

- , - example_array. realloc().

Answer 4

, std::vector . , , , . .

, . , Example , , . , , . , , , , ( , ).

, capacity() reserve() .

#include <vector>

int function_1(int a, int b) {
    return 100;
}

int function_2(int a, int b) {
    return 200;
}

typedef struct  {
    int name;
    int (*func)(int, int);
    int bool_switch;
} example_t;

typedef std::vector<example_t> example_container_t;

int main() {
    example_container_t container;

    example_t example_1;
    example_1.name = 1;
    example_1.func = &function_1;
    example_1.bool_switch = true;
    container.push_back(example_1);

    example_t example_2;
    example_2.name = 1;
    example_2.func = &function_1;
    example_2.bool_switch = true;
    container.push_back(example_2);
    return 0;
}