A function to read a string of unknown length from stdin in C.

get_str.c

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

char *get_str(void)
{
    char *str = malloc(sizeof (char));

    if (!str) {
        printf("\nUnable to allocate memory.\n");
        exit(EXIT_FAILURE);
    }

    size_t index = 0;
    size_t length = 1;
    
    while (true) {
        int temp_char = getc(stdin);
        
        if ((temp_char == '\n') || (temp_char == EOF)) {
            str[index] = '\0';
            return str;
        }
        
        str[index] = (char)temp_char;
        index++;
        length++;

        char *temp_str = realloc(str, length * sizeof (char));

        if (!temp_str) {
            printf("\nUnable to reallocate memory.\n");
            exit(EXIT_FAILURE);
        }

        str = temp_str;
    }
}