Question

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.

Answer 1

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().

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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; }