realloc() invalid pointer error when increasing size of string in a function

Question

When i run code it show realloc() invalid pointer error.

Is anything wrong in input() function?

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>
char *input(void)
{
    int n = 1;
    char *str = malloc(sizeof(char));
    *str = '\0';
    while((*str=getchar())!='\n')
    {
        n++;
        str = realloc(str,sizeof(char)*n);
        str++;
    }
    return str;
}

int main(int argc, char const *argv[])
{
    char *str = input();
    printf("%s",str);
    free(str);
    return 0;
}

Answer 1

You make a few errors:

• you return the end of the string, not the beginning.

• realloc needs the original address (see Thomas' answer)

• realloc may return a new address

• you do not terminate the string.

The following fixes these errors and includes some suggestions:

char *input(void)
{
    size_t i=0;
    int c;
    char *str = malloc(1);
    if (!str) return 0;
    while((c=getchar())!=EOF && c!='\n')
    {
        str[i]= c;
        if ((newstr = realloc(str,i+1))==0)
            break;          // out of memory: return what we have
        str= newstr;
        i++;
    }
    str[i]= '\0';
    return str;
}