Monthly Archive for February, 2009

dynamic_fgets: Reading long input lines in C

Accepting lines of input that are arbitrarily long is not something the C standard library was designed for. However, it can be an immensely useful feature to have. I recently came across this problem while rewriting the file input parts of libbitconvert. Here’s my solution, modeled after the C standard library’s fgets:

int dynamic_fgets(char** buf, int* size, FILE* file)
	char* offset;
	int old_size;

	if (!fgets(*buf, *size, file)) {

	if ((*buf)[strlen(*buf) - 1] == 'n') {
		return 0;

	do {
		/* we haven't read the whole line so grow the buffer */
		old_size = *size;
		*size *= 2;
		*buf = realloc(*buf, *size);
		if (NULL == *buf) {
		offset = &((*buf)[old_size - 1]);

	} while ( fgets(offset, old_size + 1, file)
		&& offset[strlen(offset) - 1] != 'n' );

	return 0;

And here is an example of how to use it:

char* input;
int input_size = 2;
int rc;

input = malloc(input_size);
if (NULL == input) { return BCERR_OUT_OF_MEMORY; }
rc = dynamic_fgets(&input, &input_size, stdin);
if (BCERR_OUT_OF_MEMORY == rc) { return rc; }
/* use input */

To show you how dynamic_fgets works, I’ll break into down line by line and then describe some of its features:
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Moonlight and the Microsoft Media Pack

You may have heard that Moonlight, the free software Silverlight plugin for GNU/Linux distributions, allows users to view certain audio and video encoded with Microsoft codecs. What may be confusing, though, is how you can do this if Moonlight is free software since the Microsoft codecs are patented (see “The codec dilemma” for details). I dug into this a bit and here’s what I found:
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Libre x86 C compilers for Unix-like systems

In the quest to ensure my C code is as portable as possible and, in particular, does not depend on any gcc extensions, I did some looking for C compilers that work on Unix-like x86 (32-bit) systems, are libre (“free as in freedom”), and support C89. Here is a list of the compilers I found that meet this definition and some of the caveats and benefits of each:
Continue reading ‘Libre x86 C compilers for Unix-like systems’