Thread: New programmer - reading in a large expression

...you're creating several memory leaks. Congratulations.

Is it me or was this sarcastic ?

You can try using realloc. And you should check if it returns NULL before making any operation on the pointer returned (else, you'll have something you know well, a segmentation error)

But this will be rather slow if you use realloc every time you read a character. Would be better to realloc memory every 100 characters (or more) you read in. Or you could start by allocating a certain amout of memory, let's say for X characters, than if the number of characters you read is bigger, you reallocate some, etc...

But why do you need those characters to be stored in a string, ie what's the problem you are trying to resolve ?

Another solution would be to use a file to store the characters, since you can acces elements in file quite the "same way" (ie. direct acces) than in memory. Can be useful in some situations where you don't need all the elements at a time in memory. But you need somehow a good knowledge if you want to do something who makes sense.

That code dosn't give you want you want. perhaps that wont even compile. What you have to do allocate memory using malloc. And fi you want to extend the allocated memory then use realloc not just staright way using it.

So go and allocate memory for temp using malloc

Code:

char *temp = malloc(sizeof(char) * 100);

And now if your want 100 more bytes do this

Code:

char temp1 = realloc(temp, strlen(temp) + 101);
if(temp != NULL)
   temp = temp1;

Please make sure u check the return vallue of malloc.

ssharish

scanf is dangerous.
Your program can be overflowed and this way you can arrange, without even knowing, a really big mess.
As Aia said, use fgets.
fgets works this way.

Code:

fgets(var, maximumNum, stdin); // This is an example how to get the user's input;

e.g:

Code:

char name[10];
printf("Enter your name please:\n");
fgets(name, 10, stdin);
printf("%s", name); // or fputs(name, stdout); or many other ways, lol

EDIT: Ahh! fgets & fputs works only for strings.

and just for the record, gets is also dangerous.

I'm curious to know...

1. Where does the input come from? Is it from the keyboard ? Is it from a file ?
2. When you say "a very large expression", what does that means exactly. What kind of input your program is suposed to work on ? What are those "expression" ?
3. Which treatment do you have to do on that expression, ie why do you need absolutely an array.

Maybe we'll be able to give you more help knowing that. Because if your only goal is to take input from keyboard, store it in an array, well, here's some working code

Code:

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

#define NB_ELEM_INI 100000
#define INCREM 1000

int main()
{
    char c;
    char *tab;
    size_t tailleTab = NB_ELEM_INI;
    size_t cardTab = 0;

    tab = malloc(tailleTab * sizeof(char));
    if (tab == NULL)
    {
        printf(" Error: not enough memory\n");
    }

    else
    {
        while (((c = getchar()) != '\n') && (tab != NULL))
        {
            if (cardTab == tailleTab)
            {
                tailleTab = tailleTab + INCREM;
                tab = realloc(tab, tailleTab);
                if (tab == NULL)
                {
                    printf(" Error: not enough memory\n");
                }

                else
                {
                    tab[cardTab] = c;
                    cardTab++;
                }
            }

            else
            {
                tab[cardTab] = c;
                cardTab++;
            }
        }

        // Append the zero
        if (tab != NULL)
        {
            if (cardTab == tailleTab)
            {
                // Insert the '\0' on the last character read since i'm lazy
                cardTab--;
            }

            tab[cardTab] = '\0';
        }

        // You might think freeing the memory here
        free(tab);
    }

    return 0;
}

Didn't test. Should work. Variables name are mostly in french. By the way this should be somehow inefficient, but it should work. There's better way to do so.

Originally Posted by 9988776655

Hi i need to read an expression that is very large and stuff it in a string. I dont know how long the expression is but it can be over 1 million characters.

Over 1 million characters!? Holy crap!
Do you have a million monkeys sitting infront of a million keyboards or something?

Most programs aren't even a million characters, let alone a single expression... What on earth could you possibly be doing?