How would you optimize this code? (Memory allocation for character input)

**JorgeChemE** · 06-14-2017

This is maybe the last exercise I will do of my course (yet finished). We have 6 exercises that our instructor left in the last class, 6 exercises about memory allocation, this is the fourth one.

Statement: Insert characters through keyboard one by one; the program must ask Y/N choice to continue inserting characters (one by one). Use realloc function for memory allocation. The program must print all the characters inserted.

I have been working in the program. I am not lazy at least, you know. I tried to solve it and I'm happy, I solved it. The code works "like a charm" but I want to use the correct code according to your recommendations. Please, don't blame me too much, I promise you I am making the effort to go to the right way, but still I need more practice. I am using some code thanks to laserlight. I know there is room for improvements, that's the reason I'm posting the code here. Compiled in C

Now, the code:

Code:

#include <stdio.h>#include <stdlib.h>
#include <string.h>
#define MAX_SIZE 10//No magic numbers, I take your advice seriously men.


int main()
{
    int cont=0;
    char *ptr;//Pointer to store characters
    char c;
    char choice;//Character to read (Y/N)


    ptr=calloc(MAX_SIZE, sizeof(char));//Allocate at least 10 characters


    if (!ptr) {//Laserlight code, finally understood EXIT_FAILURE
        fprintf(stderr, "There is not enough memory.\n");
        return EXIT_FAILURE;
    }


    do {//do while loop to work the loop at least once
        printf("Insert a character: ");
        scanf(" %c", &c);//I accept more efficient alternatives
        ptr=realloc(ptr, MAX_SIZE * sizeof(*ptr));//re-allocate (resize) memory for character read to be stored

        if (!ptr) {//Laserlight code again for re-allocating
            fprintf(stderr, "La realocacion ha fallado por falta de memoria.\n");
            return EXIT_FAILURE;
        }
        printf("Insert more characters: (Y/N)");//To insert character one by one
        scanf(" %c", &choice);
        ptr[cont++]=c;//Advance in the loop
    } while (choice=='Y' || choice=='y');//While user press Y but also consider y, I took case sensitive in consideration


    ptr[strcspn(ptr, "\n")] = '\0';//Laserlight code
    printf("The characters inserted are: %s\n", ptr);
    free(ptr);//Free memory at the end of the program


    return 0;
}

Anny advice to make it better would be greatly appreciated. Only in C, not C++, I compiled in C and I'm working in C and I'm in C forum. Now I'm thinking, free is correctly placed? should I put another free above after calloc?

I feel like the Cristiano Ronaldo of programming

. No, no, that was a joke to calm the environment.

**Salem** · 06-14-2017

Your realloc isn't making the memory any bigger, because you're not changing the size.

Code:

size_t used = 0;  // how much you've used
size_t maxAvailable = 0 ; // how much is actually available
char *ptr = NULL; // where we're storing the data
// setting ptr to NULL means we don't have to have an initial malloc

// .. your loop

// Every time you want to add something to ptr, do this
if ( used == maxAvailable ) {
  // the new size is 16 the first time around, or double what it was last time
  // something like newMax = maxAvailable+1 would cause thrashing - don't do it
  size_t newMax = maxAvailable == 0 ? 16 : (maxAvailable * 2);

  // cannot use ptr yet, realloc might fail - but ptr would still be valid
  void *temp = realloc( ptr, newMax * sizeof(*ptr) );
  if ( temp ) {
    // success!
    ptr = temp;
    maxAvailable = newMax;
  } else {
    // failure
    // print error message
    // do something with ptr
    // do NOT go onto do ptr[used++] below
  }
}

// now update memory
ptr[used++] = c;

> while (choice=='Y' || choice=='y');
Where do you input choice?

**JorgeChemE** · 06-14-2017

Excuse me for double post. I thought it failed after submitting.

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