Thread: Problems with dynamic memory and strings

Hi everyone! I've started learning C a couple of months ago and now I'm facing a couple of problems when it comes to dynamic memory.
You see, I was trying to make a program that could read as many characters as the user would type. Everything was working fine but I couldn't print out the whole string. Any suggestions would be very much appreciated

Thanks in advance!

Code:

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


int main ()
{
 char *c = (char*)malloc(sizeof(char));
 int x = 0;
 do
 {
     c = (char*)realloc(c, sizeof(char)*(x+1));
     *(c+x) = getchar();
     x++;
 }while (*(c+x) != '\0');


for (int y = 0; y < x; y++ )
 {
   printf("%c", c[y]);
 }
 getch();
}

A few things.

*(c+x) can be written c[x], which tends to be easier to read.

getchar() does not return '\0' to mean “end of input”. Rather, it returns EOF; if you want to stop when the user hits enter, then you need to check for '\n'.

However, due to the way getchar() works, if you want to check for EOF, you have to assign to an int first, as in:

Code:

int character = getchar();
if(character != EOF) /* do something with it */

In the current code, when you check against '\0', you're not looking at the character the user just entered, becuase you've incremented x already. What you're basically doing is this:

Code:

c[x] = whatever;
x++;
if(c[x] == '\0')

But see how c[x] doesn't hold any value? You've not written anything there; c[x - 1] is the last character written.

It's also not necessary in C to cast the return value of malloc(). malloc() returns void* which can be converted, without a cast, to any object pointer type, such as char*.

Thank you so much cas! I didn't notice that problem with 'x'. I have to pay more attention while coding. Now it's working properly.

By the way, I do have to cast the return value of malloc, otherwise I get an error when I compile the program

By the way, I do have to cast the return value of malloc, otherwise I get an error when I compile the program

Then you're either using a C++ compiler or a terrible C compiler. I'd guess the former. If you're learning C, configure your compiler to be a C compiler not C++ (it might be as easy as naming the file something.c instead of something.cpp).