23 April 2011

Strange C sizeof(struct) results?

If you wonder, why sizeof operator returns values bigger than you expect, you probably have to learn about compiler data structure alignment(as I had to:). Here I post a simple program demonstrating the case.


#include <stdio.h>
#include <string.h>

typedef struct 
#ifdef PACKED 
__attribute__ ((packed)) 
    char *str;      // 8
    char ch ;       // 1
    int a;          // 4
    int b;          // 4
    int c;          // 4
    // Packed total size should be: 21
    // Aligned total size should be: 24
} test_t;

static void print_sizes(test_t *t)
    printf("DATA TYPE SIZES\n");
    printf("char*: %ld\n", sizeof(char*));
    printf("char: %ld\n", sizeof(char));
    printf("int: %ld\n", sizeof(int));

    printf("\nSIZE OF *t: %ld\n", sizeof(*t));

int main (int argc, char const* argv[]) {
    test_t t;
    t.str = "test string"; 


    return 0;


ifeq ($(PACKED), true)

ifdef OUT

CFLAGS=-Wall -c $(PACK)

all: test

test: main.o
    $(CC) main.o -o $(OUT) 

main.o: main.c
    $(CC) $(CFLAGS) main.c -o main.o

    rm -f *.o *~

Compile versions with packed and padded memory:

$ make PACKED=true OUT=test_packed
$ make OUT=test_padded

and test them:
$ ./test_packed
char*: 8
char: 1
int: 4

SIZE OF *t: 21

$ ./test_padded
char*: 8
char: 1
int: 4

SIZE OF *t: 24

So one should consider a space-time tradeoff for every particular program.

I'd be glad, if it helps someone.

19 April 2011

How to add new highlight mode in GEdit

Here I show common steps to create custom language for GtkSourceView 2.0(GEdit uses it to display code). Then we'll create MBox language and special highlighting for it.

Common steps

1. Make directories for language definition and for new MIME:

$ mkdir -p ~/.local/share/gtksourceview-2.0/language-specs/
$ mkdir -p  ~/.local/share/mime/packages/

2. Create new MIME definition in ~/.local/share/mime/packages/

3. Create .lang file in ~/.local/share/gtksourceview-2.0/language-specs/

4. Update MIME database

$ update-mime-database ~/.local/share/mime

New language for MBox

STEP - 2: New MIME
Actually it should be already in /usr/share/mime/application/mbox.xml. But one would probably override it:

$ cat > ~/.local/share/mime/packages/mbox.xml
Author:     Ruslan Osmanov
Date:       Tue Apr 19 05:12:58 UTC 2011
Version:    1.0
<mime-info xmlns='http://www.freedesktop.org/standards/shared-mime-info'>
    <mime-type type="application/mbox">
        <comment>MBox Source</comment>
        <magic priority="50">
            <match type="string" offset="0" value="&gt;"/>
        <glob pattern="*.mbox"/>
^D stands for Ctrl + D shortcut.

STEP - 3: New Language Definition

The GNOME Language Definition Reference 2.0[1] and Language Definition v2.0 Tutorial [2] are good start points.
Syntax highlighting styles could be found in /usr/share/gtksourceview-2.0/styles/.

This info is quite enought to implement a new language:

$ cat > ~/.local/share/gtksourceview-2.0/language-specs/mbox.lang
<?xml version="1.0" encoding="UTF-8"?>
Author: Ruslan Osmanov 
Date:   Mon Apr 18 17:08:52 UTC 2011
Version:   1.0
MBox language spec
<language id="mbox" _name="MBox" version="2.0" _section="Email">
 <property name="mimetypes">text/x-mbox;application/mbox</property>
 <property name="globs">*.mbox</property>
 <property name="line-comment-start">&gt;</property>
 <style id="keyword" _name="Keyword" map-to="def:keyword"/>
 <style id="underlined" _name="Underlined" map-to="def:underlined"/>
 <style id="comment" _name="Comment" map-to="def:comment"/>
 <style id="string" _name="A string" map-to="def:string"/>
 <context id="mbox">
  <context id="keyword" style-ref="keyword">
    <suffix>( |\:)</suffix>
    <!-- Russian -->
  <context id="link" style-ref="underlined">
  <context id="comment" style-ref="comment">
   <context ref="link"/>
  <context id="comment-multiline" style-ref="comment">
   <context ref="def:in-comment"/>
  <context id="string" end-at-line-end="true" style-ref="string">

<!--vim: set ft=xml:-->

Note, ^D stands for Ctrl + D shortcut.

STEP - 4. Update MIME database

$ update-mime-database ~/.local/share/mime

Voila! You now have new MBox language in View - Highlight Mode - Email section.


08 April 2011

Change indentation: spaces to tabs

To convert space indentation in significant number of files, you may use the
following script.

#!/bin/bash - 
#          FILE:  fixtab.sh
#         USAGE:  ./fixtab.sh <directory>
#   DESCRIPTION:  Convert expanded tabs into tabs with 4 space width
#       OPTIONS: $1 directory
#        AUTHOR: Ruslan Osmanov 
#       CREATED: 04/08/2011 03:26:00 PM UZT
set -o nounset                              # Treat unset variables as an error


function usage(){
 echo "bash $0 <directory>"

[[ ! -d $DIR ]] && usage

# Correct existing modelines I used to include modelines beginning from set
# expandtab, so this worked for me. If you don't use modelines, comment it out 
find $DIR -name *.php -exec \
 sed -i -e 's%# vim: set expandtab:%# vim: set noet:%g' {} \;

# Retab & format source code
find $DIR -name *.php -exec \
 vim -u NONE \
 -c 'set ft=php' \
 -c 'set shiftwidth=4' \
 -c 'set tabstop=4' \
 -c 'set noexpandtab!' \
 -c 'set noet' \
 -c 'retab!' \
 -c 'bufdo! "execute normal gg=G"' \
 -c wq \
 {} \;

For example:
$ bash ./fixtab.sh /srv/www/myproject
I would be glad, if this helped somebody.