Using Malloc for i endless C -String

Question

I was wondering is it possible to create one endless array which can store endlessly long strings?

So what I exactly mean is, I want to create a function which gets i Strings with n length.I want to input infinite strings in the program which can be infinite characters long!

void endless(int i){
     //store user input on char array i times 
}

To achieve that I need malloc, which I would normally use like this:

string = malloc(sizeof(char));

But how would that work for lets say 5 or 10 arrays or even a endless stream of arrays? Or is this not possible?

Edit: I do know memory is not endless, what I mean is if it where infinite how would you try to achieve it? Or maybe just allocate memory until all memory is used?

Edit 2: So I played around a little and this came out:

void endless (char* array[], int numbersOfArrays){
int j;

//allocate memory
for (j = 0; j < numbersOfArrays; j++){
    array[j] = (char *) malloc(1024*1024*1024);
}

//scan strings
for (j = 0; j < numbersOfArrays; j++){
    scanf("%s",array[j]);
    array[j] = realloc(array[j],strlen(array[j]+1));
}

//print stringd
for (j = 0; j < numbersOfArrays; j++){
    printf("%s\n",array[j]);
}
}

However this isn't working maybe I got the realloc part terrible wrong?

Answer 1

Here is a toy example program that asks the user to enter some strings. Memory is allocated for the strings in the get_string() function, then pointers to the strings are added to an array in the add_string() function, which also allocates memory for array storage. You can add as many strings of arbitrary length as you want, until your computer runs out of memory, at which point you will probably segfault because there are no checks on whether the memory allocations are successful. But that would take an awful lot of typing.

I guess the important point here is that there are two allocation steps: one for the strings and one for the array that stores the pointers to the strings. If you add a string literal to the storage array, you don't need to allocate for it. But if you add a string that is unknown at compile time (like user input), then you have to dynamically allocate memory for it.

Edit:

If anyone tried to run the original code listed below, they might have encountered some bizarre behavior for long strings. Specifically, they could be truncated and terminated with a mystery character. This was a result of the fact that the original code did not handle the input of an empty line properly. I did test it for a very long string, and it seemed to work. I think that I just got "lucky." Also, there was a tiny (1 byte) memory leak. It turned out that I forgot to free the memory pointed to from newstring, which held a single '\0' character upon exit. Thanks, Valgrind!

This all could have been avoided from the start if I had passed a NULL back from the get_string() function instead of an empty string to indicate an empty line of input. Lesson learned? The source code below has been fixed, NULL now indicates an empty line of input, and all is well.

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

char * get_string(void);
char ** add_string(char *str, char **arr, int num_strings);

int main(void)
{
    char *newstring;
    char **string_storage;
    int i, num = 0;

    string_storage = NULL;

    puts("Enter some strings (empty line to quit):");
    while ((newstring = get_string()) != NULL) {
        string_storage = add_string(newstring, string_storage, num);
        ++num;
    }

    puts("You entered:");
    for (i = 0; i < num; i++)
        puts(string_storage[i]);

    /* Free allocated memory */
    for (i = 0; i < num; i++)
        free(string_storage[i]);
    free(string_storage);

    return 0;
}

char * get_string(void)
{
    char ch;
    int num = 0;
    char *newstring;

    newstring = NULL;
    while ((ch = getchar()) != '\n') {
        ++num;
        newstring = realloc(newstring, (num + 1) * sizeof(char));
        newstring[num - 1] = ch;
    }
    if (num > 0)
        newstring[num] = '\0';

    return newstring;
}

char ** add_string(char *str, char **arr, int num_strings)
{
    ++num_strings;
    arr = realloc(arr, num_strings * (sizeof(char *)));
    arr[num_strings - 1] = str;

    return arr;
}

Answer 2

I was wondering is it possible to create one endless array which can store endlessly long strings?

The memory can't be infinite. So, the answer is NO. Even if you have every large memory, you will need a processor that could address that huge memory space. There is a limit on amount of dynamic memory that can be allocated by malloc and the amount of static memory(allocated at compile time) that can be allocated. malloc function call will return a NULL if there is no suitable memory block requested by you in the heap memory.

Assuming that you have very large memory space available to you relative to space required by your input strings and you will never run out of memory. You can store your input strings using 2 dimensional array.

C does not really have multi-dimensional arrays, but there are several ways to simulate them. You can use a (dynamically allocated) array of pointers to (dynamically allocated) arrays. This is used mostly when the array bounds are not known until runtime. OR

You can also allocate a global two dimensional array of sufficient length and width. The static allocation for storing random size input strings is not a good idea. Most of the memory space will be unused.

Also, C programming language doesn't have string data type. You can simulate a string using a null terminated array of characters. So, to dynamically allocate a character array in C, we should use malloc like shown below:

char *cstr = malloc((MAX_CHARACTERS + 1)*sizeof(char));

Here, MAX_CHARACTERS represents the maximum number of characters that can be stored in your cstr array. The +1 is added to allocate a space for null character if MAX_CHARACTERS are stored in your string.

Answer 3

The memory is not infinite, thus you cannot.

I mean the physical memory in a computer has its limits.

malloc() will fail and allocate no memory when your program requestes too much memory:

If the function failed to allocate the requested block of memory, a null pointer is returned.

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Assuming that memory is infinite, then I would create an SxN 2D array, where S is the number of strings and N the longest length of the strings you got, but obviously there are many ways to do this! ;)

Another way would be to have a simple linked list (I have one in List (C) if you need one), where every node would have a char pointer and that pointer would eventually host a string.

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You can define a max length you will assume it will be the max lenght of your strings. Otherwise, you could allocate a huge 1d char array which you hole the new string, use strlen() to find the actual length of the string, and then allocate dynamically an array that would exactly the size that is needed, equal of that length + 1 for the null-string-terminator.