Stripping a sentence for only it's alpha characters

I'm trying to solve a code to strip a sentence down only to it's alpha character, using the following code, but the code always gives me a runtime error(The commented parts are steps I had taken to figure out the solution).
[Ex: Test'sen- tence should print Testsentence]

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define BUFFER_LEN 1000

#define BUFFER_INCR 15

int main(void)
{
    int buffer_length = BUFFER_LEN;
    char *pString = malloc(BUFFER_LEN);/* initial array */
    char *pTemp_start = pString;
    long long int String_len = 0;
    char *pTemp = NULL;
    int copy = 0;
    int count = 0;/*delete this after check*/

while((*pString++ = getchar()) != '\n')
{
    String_len = pString - pTemp_start;
    printf("\nThe character you inputted is: %c", *(pString+count++));
    //getchar();

    if(String_len == (buffer_length - 1))/*reserve one for newline*/
    {
        buffer_length += BUFFER_INCR;
        pTemp = realloc(pString, buffer_length);/*reallocate space for 
                                                    15 more chars.*/
        pTemp_start = pTemp - String_len;
        pString = pTemp;
        free(pTemp);
        pTemp = NULL;
        if(!pString)
        {
            printf("The space couldn't be allocated");
            return 1;
        }
    }
}



/*checks that can be done for addresses*/
//printf("\nThe length of the string is: %lld", pString - pTemp_start);
*(--pString) = '\0';
//printf("\nThe charcter at the end is: %d", *(pString + String_len - 1)); 
//printf("\nThe character at the mid is: %d", *(pString + 2));


printf("The input string is: %c", *pString);

/*code to remove spaces*/
for(int i = 0; i < (String_len + 1); i++)
{
    if((isalnum(pString[i])))
    {

        *(pString + copy++) = *(pString +i);
    }
}

*(pString + copy) = '\0';/*append the string's lost null character*/


printf("\nThe stripped string is: \n%s", pString);

return 0;


}

The code simply doesn't print anything that's inputted.

Solution

So you've got a conflict in your code between this line

while((*pString++ = getchar()) != '\n')

and lines like the following.

pTemp = realloc(pString, buffer_length);

The first line I've quoted is incrementing the position of pString within your allocated memory, but the second one is acting as if pString is still pointing to the start of it. realloc() won't work unless pString is pointing to the start of the allocated memory. You're then not checking the results of the realloc() call, assigning the new memory block to pString and then freeing the newly allocated memory. So you're definitely going to have unexpected results.

You also have to remember that stdin is buffered, so your code will wait until it's got an entire line to read before doing anything. And stdout is also buffered, so only lines that end in a \n will be output. So you probably want to have the following...

printf("The character you inputted is: %c\n", *pString);

...or something similar bearing in mind the issues with how you're using pString.