C: read string into dynamic array - c

Question

Hi im trying to read user input of "unlimited" length into an char array. It works fine for shorter strings, but for more than around 30 characters the programm crashes. Why does this happen and how can i fix this?
#include <stdio.h>
#include <stdlib.h>
char* read_string_from_terminal()//reads a string of variable length and returns a pointer to it
{
int length = 0; //counts number of characters
char c; //holds last read character
char *input;
input = (char *) malloc(sizeof(char)); //Allocate initial memory
if(input == NULL) //Fail if allocating of memory not possible
{
printf("Could not allocate memory!");
exit(EXIT_FAILURE);
}
while((c = getchar()) != '\n') //until end of line
{
realloc(input, (sizeof(char))); //allocate more memory
input[length++] = c; //save entered character
}
input[length] = '\0'; //add terminator
return input;
}
int main()
{
printf("Hello world!\n");
char* input;
printf("Input string, finish with Enter\n");
input = read_string_from_terminal();
printf("Output \n %s", input);
return EXIT_SUCCESS;
}

Answer 1

realloc(input, (sizeof(char))); //allocate more memory only allocates 1 char. Not 1 more char. #MikeCAT
(sizeof(char)*length+1) is semantically wrong. Should be (sizeof(char)*(length+1)), but since sizeof (char) == 1, it makes no functional difference.
Need space for the null character. #MikeCAT
Should test for reallocation failure.
char c is insufficient to distinguish all 257 different responses from getchar(). Use int. getchar() may return EOF. #Andrew Henle
Minor: Better to use size_t for array indexes than int. int maybe too narrow.
In the end code needs to do something like:
size_t length = 0;
char *input = malloc(1);
assert(input);
int c;
...
while((c = getchar()) != '\n' && c != EOF) {
char *t = realloc(input, length + 1);
assert(t);
input = t;
input[length++] = c;
}
...
return input;
int main(void) {
...
input = read_string_from_terminal();
printf("Output \n %s", input);
free(input);
return EXIT_SUCCESS;
}