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Top Forums Programming C: inputting string of unknown length Post 303040985 by DevuanFan on Monday 11th of November 2019 03:54:15 PM
Old 11-11-2019
C: inputting string of unknown length

I realize this general issue (inputting strings of variable length in C) has been addressed in myriad locations before, but I'm interested in knowing why my specific approach is not working. (BTW I'm intentionally keeping the size increments small so that I can more easily follow what's going on. After it works on a small scale, I can increase the size to something more reasonable. The main motivation for this approach is that I want to increase the size by a fixed increment, not by doubling the allocated memory each time.)

Here is the code:
Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define SIZE 4

int main(void)
{
	int mem = SIZE;
	char *str = malloc(mem); // let's keep str pointing to beginning of string...
	char *next_read = str; // ...and next_read pointing to where next character should go

	fgets(next_read, mem, stdin);
	next_read--; // so that after we add SIZE to pointer, it points to current '\0'

	while(str[strlen(str)-1] != '\n') // if we got whole string, the last char will be '\n'
	{
		mem += SIZE;
		str = realloc(str, mem); 
		next_read += SIZE;
		fgets(next_read, SIZE+1, stdin); // read the rest (hopefully) of the line into the new space
		printf("str is now %s\n", str);
	}

	printf("final str is %s", str);
	// free(str);
	return 0;
}

The code works fine for short strings, but stops working (program seems to get stuck) if string is longer:
Code:
bruno@thinkpad:~/Desktop434$ gcc getstring.c 
bruno@thinkpad:~/Desktop436$ ./a.out 
I love linux
str is now I love 
str is now I love linu
str is now I love linux

final str is I love linux
bruno@thinkpad:~/Desktop436$ ./a.out 
I love linux and the C programming language
str is now I love 
str is now I love linu
str is now I love linux an
str is now I love linux and th
str is now I love linux and the C 
str is now I love linux and the C 
str is now I love linux and the C 
str is now I love linux and the C 
str is now I love linux and the C 
str is now I love linux and the C 
str is now I love linux and the C

I'm a newbie in C and would like to learn something by debugging this.

Last edited by DevuanFan; 11-11-2019 at 05:00 PM..
 

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MARC::Charset::Code(3pm)				User Contributed Perl Documentation				  MARC::Charset::Code(3pm)

NAME
MARC::Charset::Code - represents a MARC-8/UTF-8 mapping SYNOPSIS
DESCRIPTION
Each mapping from a MARC-8 value to a UTF-8 value is represented by a MARC::Charset::Code object in a MARC::Charset::Table. METHODS
new() The constructor. name() A descriptive name for the code point. marc() A string representing the MARC-8 bytes codes. ucs() A string representing the UCS code point in hex. charset_code() The MARC-8 character set code. is_combining() Returns true/false to tell if the character is a combining character. to_string() A stringified version of the object suitable for pretty printing. char_value() Returns the unicode character. Essentially just a helper around ucs(). marc_value() The string representing the MARC-8 encoding. charset_name() Returns the name of the character set, instead of the code. to_string() Returns a stringified version of the object. marc8_hash_code() Returns a hash code for this Code object for looking up the object using MARC8. First portion is the character set code and the second is the MARC-8 value. utf8_hash_code() Returns a hash code for uniquely identifying a Code by it's UCS value. default_charset_group Returns 'G0' or 'G1' indicating where the character is typicalling used in the MARC-8 environment. get_marc8_escape Returns an escape sequence to move to the Code from another marc-8 character set. charset_value Returns the charset value, not the hex sequence. perl v5.12.4 2010-03-29 MARC::Charset::Code(3pm)
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