07-08-2008
Thanks for the reply. I think I know why the segfault happened, having to do with the logic of my program and the fact that I changed a bit of it to try giving 'getline' a smaller character string; I won't bore you with all the details.
While looping through a file, reading one line at a time, I should just need to call 'free' once, after the loop is through, correct? It's doing a 'realloc' when it needs more room, and not allocating a whole new string each time. I'm wondering about how much more space it reallocs when it's necessary. I just ran my program again checking the return value of 'n', size of buffer returned, and the value of bytes that were read (my initial value of the size of line is 25, just picking one that would be too small most of the time):
bytes read size of buffer returned
7 25
56 57
36 57
97 114
70 114
23 114
39 114
Apparently, once the buffer being passed back gets a certain size, it won't get reallocated to a smaller size, what with it staying at 114. I'm wondering why when the line was 96 bytes it didn't return a buffer of size 97 (allowing for the null) instead of jumping to 114.
Thanks again.
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LEARN ABOUT REDHAT
getdelim
GETLINE(3) Linux Programmer's Manual GETLINE(3)
NAME
getline, getdelim - delimited string input
SYNOPSIS
#define _GNU_SOURCE
#include <stdio.h>
ssize_t getline(char **lineptr, size_t *n, FILE *stream);
ssize_t getdelim(char **lineptr, size_t *n, int delim, FILE *stream);
DESCRIPTION
getline() reads an entire line, storing the address of the buffer containing the text into *lineptr. The buffer is null-terminated and
includes the newline character, if a newline delimiter was found.
If *lineptr is NULL, the getline() routine will allocate a buffer for containing the line, which must be freed by the user program. Alter-
natively, before calling getline(), *lineptr can contain a pointer to a malloc()-allocated buffer *n bytes in size. If the buffer is not
large enough to hold the line read in, getline() resizes the buffer to fit with realloc(), updating *lineptr and *n as necessary. In either
case, on a successful call, *lineptr and *n will be updated to reflect the buffer address and size respectively.
getdelim() works like getline(), except a line delimiter other than newline can be specified as the delimiter argument. As with getline(),
a delimiter character is not added if one was not present in the input before end of file was reached.
RETURN VALUE
On success, getline() and getdelim() return the number of characters read, including the delimiter character, but not including the termi-
nating null character. This value can be used to handle embedded null characters in the line read.
Both functions return -1 on failure to read a line (including end of file condition).
ERRORS
EINVAL Bad parameters (n or lineptr is NULL, or stream is not valid).
EXAMPLE
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE * fp;
char * line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("/etc/motd", "r");
if (fp == NULL)
exit(EXIT_FAILURE);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu :
", read);
printf("%s", line);
}
if (line)
free(line);
return EXIT_SUCCESS;
}
CONFORMING TO
Both getline() and getdelim() are GNU extensions. They are available since libc 4.6.27.
SEE ALSO
read(2), fopen(3), fread(3), gets(3), fgets(3), scanf(3)
GNU
2001-10-07 GETLINE(3)