From bfd18a52e1baa4da7040b8df04a3f29e83b0d6b6 Mon Sep 17 00:00:00 2001 From: zlg Date: Sun, 9 Jan 2022 20:18:52 -0800 Subject: Solve Exercise 8-4: fseek() implementation --- ch8/8-04_fseek.c | 34 ++++++++++++++++++++++++++++++++++ ch8/syscalls.h | 45 ++++++++++++++++++++++++++++++++++----------- 2 files changed, 68 insertions(+), 11 deletions(-) create mode 100644 ch8/8-04_fseek.c diff --git a/ch8/8-04_fseek.c b/ch8/8-04_fseek.c new file mode 100644 index 0000000..b968ca2 --- /dev/null +++ b/ch8/8-04_fseek.c @@ -0,0 +1,34 @@ +#include +#include +#include +#include +#include +#include "syscalls.h" +/* The C Programming Language: 2nd Edition + * + * Exercise 8-4: The standard library function + * + * int fseek(FILE *fp, long offset, int origin) + * + * is identical to `lseek` except that `fp` is a file pointer instead of a file + * descriptor and the return value is an `int` status, not a position. Write + * `fseek`. Make sure that your `fseek` coordinates properly with the buffering + * done for the other functions of the library. + * + * Notes: Page 174 covers lseek, where it describes fseek's return value as 0 + * for success and non-zero for errors. + */ + +int main() { + FILE *fp = fopen("8-04_fseek.c", "r"); + if (fp == NULL) { + exit(1); + } + fseek(fp, -34L, 2); + puts(fp->base); + fflush(stdout); + fclose(fp); + return 0; +} + +/* If you see this, 8-4 works! */ diff --git a/ch8/syscalls.h b/ch8/syscalls.h index ff58db5..cda913f 100644 --- a/ch8/syscalls.h +++ b/ch8/syscalls.h @@ -66,7 +66,7 @@ int fempty(struct _flags flags) { FILE * fopen(char *name, char *mode) { int fd; FILE *fp; - if (*mode != 'r' && *mode != 'w' && *mode != 'a') { + if (*mode != 'r' && *mode != 'w' && *mode != 'a' && *mode != '+') { return NULL; } for (fp = _iob; fp < _iob + FOPEN_MAX; fp++) { @@ -77,24 +77,34 @@ FILE * fopen(char *name, char *mode) { if (fp >= _iob + FOPEN_MAX) { return NULL; } - if (*mode == 'w') { - fd = creat(name, PERMS); - } else if (*mode == 'a') { - if ((fd = open(name, O_WRONLY, 0)) == -1) { + switch (*mode) { + case '+': + if ((fd = open(name, O_RDWR, 0)) == -1) { + fd = creat(name, PERMS); + } + break; + case 'w': fd = creat(name, PERMS); - } - lseek(fd, 0L, 2); - } else { - fd = open(name, O_RDONLY, 0); + break; + case 'a': + if ((fd = open(name, O_WRONLY, 0)) == -1) { + fd = creat(name, PERMS); + } + lseek(fd, 0L, 2); + break; + default: + fd = open(name, O_RDONLY, 0); } if (fd == -1) { return NULL; } fp->fd = fd; fp->cnt = 0; - if (*mode == 'r') { + fp->flags._EOF = 0; + if (*mode == 'r' || *mode == '+') { fp->flags._READ = 1; - } else { + } + if (*mode == 'w' || *mode == '+' || *mode == 'a') { fp->flags._WRITE = 1; } return fp; @@ -220,3 +230,16 @@ int puts(char *s) { putchar('\n'); return i; } + +/* Set the 'cursor' position within a file for read or write operations + * Returns 0 on success, EOF on error, with errno set. + */ +int fseek(FILE *fp, long offset, int origin) { + long pos; + if ((pos = lseek(fp->fd, offset, origin)) == EOF) { + return EOF; + } + _fillbuf(fp); + lseek(fp->fd, offset, origin); + return 0; +} -- cgit v1.2.3-70-g09d2 ak line correctlyzlg1-1/+1 2018-03-18add 'playlog' list filterzlg2-2/+9 This filter is used to get an idea of which games you're currently playing through, so you can prioritize games to play when you're bored and detect it when you've beaten a game but haven't marked it as such. 2018-03-13Update helpers a bitzlg1-2/+9 At present, user modification is needed to make these seamless. vgup() may need to be axed in favor of telling the user to make an alias. 2018-03-13Make VGSTASH_DB_LOCATION point to a filezlg2-21/+20 It used to point to a directory, which would then look for .vgstash.db. This behavior was kind of backwards and I don't remember why I did it that way. This change gives users more control over where they put their DB. Be sure to update your environment variable if you have it set! 2016-11-18Remove settings from helpers.shZe Libertine Gamer1-5/+0 Sourcing them in .bash_profile screws up login if they're set. 2016-11-15Correct phrasing in README.Ze Libertine Gamer1-4/+4 2016-11-13DerpZe Libertine Gamer1-0/+1 2016-11-03Improve error handling in shell scriptsZe Libertine Gamer4-3/+23 2016-10-24Correct run_again, add recursionZe Libertine Gamer1-0/+4 Loops and functions -- oh my, what a useful combination. :) 2016-10-21Add quotes to correct behavior for arglistZe Libertine Gamer1-1/+1 2016-10-14updater.sh: add recursion, error handlingZe Libertine Gamer1-43/+101 2016-10-14Correct pipe-handling behaviorZe Libertine Gamer1-1/+9 2016-10-12Clarify a method to move between platformsZe Libertine Gamer1-2/+5 Also correct a typo. ns'>-3/+24 Before, vgstash.DB.list_games() would default to 'allgames' and silently hide it when a filter wasn't found. This commit ensures that the vgstash package and CLI both indicate when an invalid filter is passed to them: * vgstash.DB.list_games() will return False on a failure to match; * vgstash_cli uses Click's Choice object to enforce the constraint 2018-10-12cli: Add zero-game import/export messageszlg2-11/+18 2018-10-10Bump to 0.3beta1 for PyPIzlg1-1/+1 2018-10-10Move tests and data to dedicated directoryzlg7-10/+26 Also tweaked the export command to report correctly. 2018-10-10cli: Add "export" commandzlg2-5/+54 The export command is like the import command; currently supporting YAML output, but ready to be expanded as needed. 2018-10-10cli: Add "import" commandzlg5-1/+76 Currently the import command will only accept YAML files, but is ready for expansion to other formats as needed. 2018-10-09Bump to 0.3alpha6 for PyPIzlg1-1/+1 2018-10-09cli: Add "notes" commandzlg2-4/+74 The "notes" command will show the user what their notes for a particular game are. The output can be piped anywhere the user wants, such as a pager or a file. If "notes" is passed with the "--edit" or "-e" flag, vgstash will open a temporary file with the game's notes already inside and edit it using the program pointed to by the EDITOR environment variable. When the editor is closed (with a successful exit status), vgstash updates the game's notes and exits. The defaults for the testing environment ("cat" for non-interactive, "vim" for interactive) may need tweaking on other operating systems. Patches for these platforms are very welcome. 2018-10-09update_game: ensure notes are also savedzlg1-2/+2 2018-10-09cli: add 'update' commandzlg3-20/+92 Two helper functions were also added to the vgstash package to ease client workflows. This commit marks the final core function necessary to manipulate a vgstash DB on the command line. 2018-10-06cli: Add "delete" commandzlg2-0/+19 Unlike the old version of vgstash, the new one does not accept row IDs as arguments for removal. Instead, it accepts two mandatory arguments: the title of the game, and the system it's on. This is in line with the database itself, using the title and system as primary keys. 2018-10-06Remove ID field from DBzlg3-38/+46 The sqlite database already uses a game's title and system as the primary keys. Row IDs are redundant. 2018-10-06cli: change "Status" heading to "Progress"zlg2-36/+40 2018-09-29Bump to 0.3alpha5 for PyPIzlg1-1/+1 2018-09-29cli: Add pretty printing to 'list' commandzlg3-17/+107 Also add the "--width" option to specify the maximum width of the table. 2018-09-08setup.py: Bump to alpha4 for PyPIzlg1-1/+1 2018-09-08cli: add '--raw' option to list commandzlg2-9/+45 Add '--raw' option to the list command, in addition to proper note expansion. Newline characters in notes are escaped to be friendly to scripting. This option may be shortened to '-r' at the user's convenience. In raw output mode, the information is formatted in plain pipe-delimited strings, one line per row: title|system|ownership|progress|notes ownership and progress are printed in their numeric form, consistent with the OWNERSHIP and PROGRESS dictionaries in the vgstash package. An empty notes field will result in a line ending with a pipe and no whitespace following it. 2018-09-08Add remaining filters to vgstash packagezlg1-2/+11 2018-09-04Update LICENSE to match setup.pyzlg1-80/+67 Whoops. 2018-09-03Branch off from master with pytest, tox, clickzlg16-778/+779 This commit is huge, but contains everything needed for a "proper" build system built on pytest + tox and a CLI built with click. For now, this branch will contain all new vgstash development activity until it reaches feature parity with master. The CLI is installed to pip's PATH. Only the 'init', 'add', and 'list' commands work, with only two filters. This is pre-alpha software, and is therefore not stable yet. 2018-03-18Flesh out filter types and ownership statuszlg3-82/+144 It's time for a refactor to a module; the functionality and interface are clashing. 2018-03-18README.mdown: break line correctlyzlg1-1/+1 2018-03-18add 'playlog' list filterzlg2-2/+9 This filter is used to get an idea of which games you're currently playing through, so you can prioritize games to play when you're bored and detect it when you've beaten a game but haven't marked it as such. 2018-03-13Update helpers a bitzlg1-2/+9 At present, user modification is needed to make these seamless. vgup() may need to be axed in favor of telling the user to make an alias. 2018-03-13Make VGSTASH_DB_LOCATION point to a filezlg2-21/+20 It used to point to a directory, which would then look for .vgstash.db. This behavior was kind of backwards and I don't remember why I did it that way. This change gives users more control over where they put their DB. Be sure to update your environment variable if you have it set! 2016-11-18Remove settings from helpers.shZe Libertine Gamer1-5/+0 Sourcing them in .bash_profile screws up login if they're set. 2016-11-15Correct phrasing in README.Ze Libertine Gamer1-4/+4 2016-11-13DerpZe Libertine Gamer1-0/+1 2016-11-03Improve error handling in shell scriptsZe Libertine Gamer4-3/+23 2016-10-24Correct run_again, add recursionZe Libertine Gamer1-0/+4 Loops and functions -- oh my, what a useful combination. :) 2016-10-21Add quotes to correct behavior for arglistZe Libertine Gamer1-1/+1 2016-10-14updater.sh: add recursion, error handlingZe Libertine Gamer1-43/+101 2016-10-14Correct pipe-handling behaviorZe Libertine Gamer1-1/+9 2016-10-12Clarify a method to move between platformsZe Libertine Gamer1-2/+5 Also correct a typo.