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Full Discussion: segmentation fault.
Top Forums Programming segmentation fault. Post 302482201 by Corona688 on Monday 20th of December 2010 11:00:47 PM
Old 12-21-2010
Well, you're going to run out of new and interesting ways to cause it soon, I'm sure... Smilie

It's not a UNIX thing, either. You'd be getting these same crashes on Windows for the same reasons, though it might call them something else.

What "segmentation fault" means is you're trying to use memory you don't have. Of all possible addresses from 0 to 0xffffffff (on 32-bit) only a small bit of those are actually valid -- those your program has asked for or been granted on load.

Code:
char output[4000000][1000];

That's a three gigabyte variable! Almost four, even. Smilie There's no way the system is going to let you have a local variable so big. On a 32-bit system it might not even be possible to get that much memory in one process by any means. So when it tries, it reaches gigabytes beyond the maximum address the OS is willing to give it, and bingo: segmentation fault.

Try something a little more modest. char output[1024][1024]; That's exactly one megabyte.

---------- Post updated at 10:00 PM ---------- Previous update was at 09:26 PM ----------

Code:
std::cout << output[cnt] << "\n" << endl;

This is redundant since the strings read in by fgets() already have a \n on the end.

Code:
std::cout << output[cnt];


Last edited by Corona688; 12-20-2010 at 11:39 PM..
 

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OD(1)                                                              User Commands                                                             OD(1)

NAME
od - dump files in octal and other formats SYNOPSIS
od [OPTION]... [FILE]... od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]] od --traditional [OPTION]... [FILE] [[+]OFFSET[.][b] [+][LABEL][.][b]] DESCRIPTION
Write an unambiguous representation, octal bytes by default, of FILE to standard output. With more than one FILE argument, concatenate them in the listed order to form the input. With no FILE, or when FILE is -, read standard input. If first and second call formats both apply, the second format is assumed if the last operand begins with + or (if there are 2 operands) a digit. An OFFSET operand means -j OFFSET. LABEL is the pseudo-address at first byte printed, incremented when dump is progressing. For OFFSET and LABEL, a 0x or 0X prefix indicates hexadecimal; suffixes may be . for octal and b for multiply by 512. Mandatory arguments to long options are mandatory for short options too. -A, --address-radix=RADIX output format for file offsets; RADIX is one of [doxn], for Decimal, Octal, Hex or None --endian={big|little} swap input bytes according the specified order -j, --skip-bytes=BYTES skip BYTES input bytes first -N, --read-bytes=BYTES limit dump to BYTES input bytes -S BYTES, --strings[=BYTES] output strings of at least BYTES graphic chars; 3 is implied when BYTES is not specified -t, --format=TYPE select output format or formats -v, --output-duplicates do not use * to mark line suppression -w[BYTES], --width[=BYTES] output BYTES bytes per output line; 32 is implied when BYTES is not specified --traditional accept arguments in third form above --help display this help and exit --version output version information and exit Traditional format specifications may be intermixed; they accumulate: -a same as -t a, select named characters, ignoring high-order bit -b same as -t o1, select octal bytes -c same as -t c, select printable characters or backslash escapes -d same as -t u2, select unsigned decimal 2-byte units -f same as -t fF, select floats -i same as -t dI, select decimal ints -l same as -t dL, select decimal longs -o same as -t o2, select octal 2-byte units -s same as -t d2, select decimal 2-byte units -x same as -t x2, select hexadecimal 2-byte units TYPE is made up of one or more of these specifications: a named character, ignoring high-order bit c printable character or backslash escape d[SIZE] signed decimal, SIZE bytes per integer f[SIZE] floating point, SIZE bytes per float o[SIZE] octal, SIZE bytes per integer u[SIZE] unsigned decimal, SIZE bytes per integer x[SIZE] hexadecimal, SIZE bytes per integer SIZE is a number. For TYPE in [doux], SIZE may also be C for sizeof(char), S for sizeof(short), I for sizeof(int) or L for sizeof(long). If TYPE is f, SIZE may also be F for sizeof(float), D for sizeof(double) or L for sizeof(long double). Adding a z suffix to any type displays printable characters at the end of each output line. BYTES is hex with 0x or 0X prefix, and may have a multiplier suffix: b 512 KB 1000 K 1024 MB 1000*1000 M 1024*1024 and so on for G, T, P, E, Z, Y. EXAMPLES
od -A x -t x1z -v Display hexdump format output od -A o -t oS -w16 The default output format used by od AUTHOR
Written by Jim Meyering. REPORTING BUGS
GNU coreutils online help: <http://www.gnu.org/software/coreutils/> Report od translation bugs to <http://translationproject.org/team/> COPYRIGHT
Copyright (C) 2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. SEE ALSO
Full documentation at: <http://www.gnu.org/software/coreutils/od> or available locally via: info '(coreutils) od invocation' GNU coreutils 8.28 January 2018 OD(1)
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