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Pointer To Structure: Understanding Element Addressing


Pointer To Structure: Understanding Element Addressing

By : MagicVlad
Date : November 17 2020, 04:28 AM
To fix this issue First, malloc() do not allocate pointers, it allocates memory for your struct, and then it returns a pointer to it. It is perfectly possible to have an uninitialized pointer, or a pointer pointing nowhere (NULL).
Second, in C there are three types of variables, regarding to allocation:
code :
my_structure_t* my_struct = malloc( sizeof(my_struct) );
my_structure_t example_struct;
my_struct = &example_struct;
printf("Base Address: %p\n", &my_struct);
printf("First Element: %p\n", &(my_struct->label));
printf("Base Address: %p\n", (void*)my_struct);
printf("First Element: %p\n", (void*)&(my_struct->label));


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Understanding a structure which contains a pointer of its own type

Understanding a structure which contains a pointer of its own type


By : Didzis Videmanis
Date : March 29 2020, 07:55 AM
it fixes the issue A pointer is just a reference to a location in memory ("address"). In the case of a node, a pointer to an instance of a node is a reference to the location in memory where that node instance is stored.
For your struct as defined, if you have an instance of a node that resides in one memory location, it can point to two other node instances that reside in their own memory locations (*llink, *rlink).
Pointer within structure reallocs fine, but pointer to a pointer within structure fails to realloc with invalid pointer

Pointer within structure reallocs fine, but pointer to a pointer within structure fails to realloc with invalid pointer


By : BenBTC
Date : March 29 2020, 07:55 AM
I wish this helpful for you While working on a program which requires frequent memory allocation I came across behaviour I cannot explain. I've implemented a work around but I am curious to why my previous implementation didn't work. Here's the situation: , First fragment:
code :
// cycle through decompressed file until end is reached
while (1) {
        char **tmp_data;
        read_size = gzread(fh, buf, sizeof buf);
        if (read_size <= 0) break;

        // allocate/reallocate memory to fit newly read buffer
        tmp_data = realloc(file->data, (file->size+read_size) * sizeof *tmp_data );
        if ( !tmp_data ) {
                printf("Memory reallocation error for requested size %d.\n"
                      , file->size+read_size);

                if (file->data) {
                        free(file->data)
                        file->data = NULL;
                        file->size = 0;
                }
                return FH_REALLOC_ERROR;
        }

        file->data = tmp_data;
        // copy data from temporary buffer
        memcpy(file->data + file->size, buf, read_size);

        // update total read file size
        file->size += read_size;
}
unsigned i; // BTW this variable is already present as args->nregexes;

for(i =0; strcmp(argv[i+regindex], "-logs"); i++) {
        char **tmp;

        tmp = realloc(args->regexes, (i+1) * sizeof *tmp ); 
        if (!tmp) {
                printf("Cannot allocate memory for regex patterns array.\n");
                return -1;
        }
        args->regexes = tmp;

        args->regexes[i] = strdup( argv[i+regindex] ); 
        if ( !args->regexes[i] ) {
                printf("Cannot allocate memory for regex pattern.\n");
                return -1;
        }
...
return 0;
}
Deallocate structure using pointer arithmetics and a pointer to an element of that structure

Deallocate structure using pointer arithmetics and a pointer to an element of that structure


By : Suranga Gunawardana
Date : March 29 2020, 07:55 AM
this will help
Can I now delete the entire object using pointer arithmetic and a pointer that points to one of the structure elements ?
understanding pointer to a structure refers to pointer member in c in accessing it

understanding pointer to a structure refers to pointer member in c in accessing it


By : Peter Hamilton
Date : March 29 2020, 07:55 AM
this one helps. I have a below program and compilation is success but while running,program crashes in eclipse , Create a Student structure, allocate it and use it
code :
typedef struct Student
{
   unsigned int  *ptr;  //Stores address of integer Variable
} Student;

int main()
{
    Student *s1;
    unsigned int roll = 20;
    s1 = malloc(sizeof(Student));
    if (s1 == NULL) {
        return -1;
    }
    s1->ptr   = &roll;

    printf("\nRoll Number of Student : %d",*(s1->ptr));
    free(s1);

    return(0);
}
Confusion in understanding Casting of a RAM address as a Pointer to structure

Confusion in understanding Casting of a RAM address as a Pointer to structure


By : Praveen.1590
Date : March 29 2020, 07:55 AM
it helps some times The C preprocessor simply does textual replacements before the actual compile process takes place:
With these defines:
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