Help with custom getline() function

Can anyone explain to me why this isn't working?

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

char *getline(int lim)
{
    char c;
    int i;
    char *line;
    line = malloc(sizeof(char) * lim);


    i = 0;
    while((c = getchar()) != '\n' && c != EOF && i < lim-1)
    {
        *line = c;
        line++;
        i++;
    }
    *line = '\0';
    printf("%s", line);
    return line;
}

I'm not worried about the return value right now - just the reason as to why printf("%s", line) isn't working.

Thanks!

EDIT: fixed to line = malloc(sizeof(char) * lim); but it is still not working.

Solution: the address of *line was being incremented throughout the function. When it was passed to printf(), *line pointed to '\0' because that's where its adress was incremented to. Using a temprorary pointer that stored the original address allocated by malloc() to *line and then passing that pointer into printf(), allowed for the function to walk up the pointer.

Solution

Because you are only allocating enough space for a single character in this line:

line = malloc(sizeof(char));

And that is getting filled with the \0 before your printf statement.

I'm guessing you want to change this line to:

/* Allocate enough room for 'lim' - 1 characters and a trailing \0 */
line = malloc(sizeof(char) * lim);

Or even better:

char *line, *tmp;
tmp = line = malloc(sizeof(char) * lim);

And then use tmp in all of your pointer math, this way line will still point to the start of your string.

And I know it's early in your development, but you'll want to make sure you free() the memory that you malloc().

Here is a working version of your function including my suggested changes:

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

char *getline(int lim)
{
    char c;
    int i;
    char *line, *tmp;
    tmp = line = malloc(sizeof(char) * lim);

    i = 0;
    /* NOTE: 'i' is completely redundant as you can use 'tmp',
     * 'line,' and 'lim' to determine if you are going to
     * overflow your buffer */
    while((c = getchar()) != '\n' && c != EOF && i < lim-1)
    {
        *tmp = c;
        tmp++;
        i++;
    }
    *tmp = '\0';
    printf("%s", line);
    return line;
}