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Exercise dump_array()

Write a generic function dump_array() that prints the content of an array to a given output stream void dump_array(const void *base, size_t num_elem, size_t elem_size, void (*dump_element)(const void *, FILE *), FILE *fp);

Where:

• base: pointer to the first element of the input array
• num_elem: number of elements of the input array
• elem_size: number of bytes taken by each element of the array
• dump_element: pointer to a function which takes a pointer to an array element as 1st argument and to an output stream as 2nd argument, and prints the input array element to the given output stream
• fp: the output stream where to print the input array

Implementation

As requested, implementation must implement 3 parts:

1 - dump_array as main function: implements a for to iterate onto elements and dump the single element

void dump_array(const void *base, size_t num_elem, size_t elem_size, void (*dump_element)(const void *, FILE *), FILE *fp)
{
    assert(base != NULL);
    assert(fp != NULL);

    const unsigned char *array = base;

    fprintf(fp, "[");
    for (int i = 0; i < num_elem; i++)
    {
        dump_element(&(array[i * elem_size]), fp); //array + i * elem_size also works
        if(i < num_elem - 1)
            fprintf(fp, ", ");
    }
    fprintf(fp, "]");
}

2 - dump_int as dumper function, passed by reference to dump_array with declaration: void (*dump_element)(const void *, FILE *)

Code consists in a cast from void * to desired type (in this case int as dump_int function) and accessing value from pointer.

//casting (implicit from void* to int*) to access value 
const int *value = p;

Implementation:

void dump_int(const void *p, FILE *fp)
{
    assert(p != NULL);
    assert(fp != NULL);
    const int *value = p; //this line is a surplus, it can be done directly casting p into *((int *)p)
    fprintf(fp, "%d", *value);
}

3 - dump_string as dumper function, passed by reference to dump_array with declaration: void (*dump_element)(const void *, FILE *)

Code consists in a cast from void * to desired type (in this case char * as dump_string function) and accessing value from pointer.

//casting (explicit) from void* to char* to access string value 
const char *temp = *((char **)p);
fprintf(fp, "%s", temp);
// can be done also passing pointer directly to fprintf
fprintf(fp, "%s", *((char **)p));

Implementation:

void dump_string(const void *p, FILE *fp)
{
    assert(p != NULL);
    assert(fp != NULL);
    const char * temp = *((char **)p); //surplus line
    fprintf(fp, "%s", temp);
}