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Full Discussion: 'getline' questions
Top Forums Programming 'getline' questions Post 302212880 by cleopard on Tuesday 8th of July 2008 04:03:20 PM
Old 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 HPUX

setlinebuf

setbuf(3S)																setbuf(3S)

NAME

       setbuf(), setvbuf(), setlinebuf() - assign buffering to a stream file

SYNOPSIS


   Obsolescent Interface
DESCRIPTION

       can  be	used after a stream has been opened but before it is read or written.  It causes the array pointed to by buf to be used instead of
       an automatically allocated buffer.  If buf is the NULL pointer input/output will be completely unbuffered.

       A constant defined in the header file, tells how big an array is needed:

       can be used after a stream has been opened but before it is read or written.  type determines how stream is to be buffered.   Legal  values
       for type (defined in are:

	      causes input/output to be fully buffered.

	      causes output to be line buffered;
			  the buffer will be flushed when a newline is written, the buffer is full, or input is requested.

	      causes input/output to be completely unbuffered.

       When  an  output stream is unbuffered, information is queued for writing on the destination file or terminal as soon as written; when it is
       buffered, many characters are saved up and written as a block.  When the output stream is line-buffered, each line of output is queued  for
       writing on the destination terminal as soon as the line is completed (that is, as soon as a new-line character is written or terminal input
       is requested).  can also be used to explicitly write the buffer.

       If buf is not the NULL pointer, the array it points to is used for buffering instead of an automatically allocated buffer (from size speci-
       fies  the  size of the buffer to be used.  The constant in is suggested as a good buffer size.  If input/output is unbuffered, buf and size
       are ignored.

       By default, output to a terminal is line buffered and all other input/output is fully buffered.

       is used to change stream from block-buffered or unbuffered to line-buffered.  can be used any time the file descriptor is active.

   Obsolescent Interface
       assigns buffering to a stream file.

DIAGNOSTICS

       If an illegal value for type or size is provided, return a non-zero value.  Otherwise, the value returned will be zero.

   Note
       A common source of error is allocating buffer space as an "automatic" variable in a code block, then failing to close  the  stream  in  the
       same block.

       Allocating a buffer of size or bytes does not necessarily imply that all of size or bytes are used for the buffer area.

AUTHOR

       and were developed by HP.

SEE ALSO

       flockfile(3S), fopen(3S), getc(3S), malloc(3C), putc(3S), stdio(3S), thread_safety(5), glossary(9).

STANDARDS CONFORMANCE

																	setbuf(3S)
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