• 2 unexploded bombs found under Ho Chi Minh City house – Approximately 800,000 tons of bombs and mines still present http://t.co/ILKjqIWX #fb ->

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• 3 Vietnamese bloggers charged over their writing | Fox News http://t.co/sFgNCYfA #fb ->

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• Implement strong WiFi encryption the easy way with hostapd – Using WPA2-Personal with individual keys for each user http://t.co/LRuke4kJ ->
• Soon, wonder vaccine that will kill 90% of cancers – Health – DNA http://t.co/AUXP0QNF ->
• PHP like str_replace function in C: This post is part of a series of posts where I want to document a bunch of C f… http://t.co/agD4GNft ->
• Kickstrap – #CSS Framework: Enhancements for Bootstrap : Kickstrap uses the latest version of Twitter's #bootstrap http://t.co/jdvbm2H4 ->

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This post is part of a series of posts where I want to document a bunch of C functions I use for my projects that I have written, collected and modified over the past few years. One of the functions that I use regularly is a string replacement function like the str_replace in PHP. This function replaces all occurences of a particular substring with a replacement pattern. The code for this was borrowed from here. In the original code, a newly allocated string is returned after all the substrings are replaced. I have modified it so that the replacements are made in place.

/**
 *
 * str_replace.c implements a str_replace PHP like function
 * Copyright (C) 2010  chantra <chantra__A__debuntu__D__org>
 *
 */

#include "str_replace.h"

void
str_replace ( char **str, const char *substr, const char *replacement ){
  char *string =  *str;
  int findlen = strlen(substr), replacelen = strlen(replacement);
  int difflen = 0, totaldiff = 0;
  char *tok = NULL;
  char *newstr = NULL;
  char *oldstr = NULL;
  char *head = NULL;
  /* if either substr or replacement is NULL, duplicate string a let caller handle it */
  if(replacelen > findlen)
    difflen = replacelen - findlen;
  if ( substr == NULL || replacement == NULL ) return;
  newstr = strdup (string);
  head = newstr;
  while ( (tok = strstr ( head, substr ))){
    oldstr = newstr;
    newstr = malloc ( strlen ( oldstr ) - strlen ( substr ) + strlen ( replacement ) + 1 );
    /*failed to alloc mem, free old string and return NULL */
    if ( newstr == NULL ){
      free (oldstr);
      exit(1);
    }
    memcpy ( newstr, oldstr, tok - oldstr );
    memcpy ( newstr + (tok - oldstr), replacement, strlen ( replacement ) );
    memcpy ( newstr + (tok - oldstr) + strlen( replacement ), tok + strlen ( substr ), strlen ( oldstr ) - strlen ( substr ) - ( tok - oldstr ) );
    memset ( newstr + strlen ( oldstr ) - strlen ( substr ) + strlen ( replacement ) , 0, 1 );
    /* move back head right after the last replacement */
    head = newstr + (tok - oldstr) + strlen( replacement );
    free (oldstr);
    totaldiff += difflen;
  }
  free(*str);
  *str = (char *) calloc(sizeof(char), (strlen(newstr) + 1));
  strcpy(*str, newstr);
  free(newstr);
  return;
}

int main(void) {
  char *string;
  string = (char *) malloc(50*sizeof(char));
  sprintf(string, "I'm a bad bad boy");
  printf("Original String - %s\n'bad' will be replaced with 'good'\n", string);
  str_replace(&string, "bad", "good");
  printf("Modified String - %s\n", string);
  free(string);
  return 0;
}

#ifndef _STR_REPLACE_H
#define _STR_REPLACE_H

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

void str_replace ( char **string, const char *substr, const char *replacement );

#endif /* _STR_REPLACE_H */

Copy the above code into str_replace.c and str_replace.h and compile it and execute it.

@~ $  make str_replace
@~ $  ./str_replace
Original String - I'm a bad bad boy
'bad' will be replaced with 'good'
Modified String - I'm a good good boy

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Kickstrap uses the latest version of Twitter’s bootstrap (http://twitter.github.com/bootstrap) and adds a layer of extras to create slick web applications with themes, modern html/css standards, an icon font, and progressive enhancement through javascript.

Kickstrap: Enhancements for Bootstrap

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• The 1% #Linux myth | Manila Standard Today http://t.co/fI83fPg6 ->
• an in-kernel x86 disassember, we can look forward to more meaningful #kernel panics now http://t.co/h4gV2qrB #fb ->
• 10 Million hits a day with WordPress using a $15 server http://t.co/3yR2BOdG ->
• Assign Google #Adsense Code to a #PHP Variable: Assigning Google Adsense code to a PHP variable doesn't work the way.. http://t.co/8i2b0Et5 ->

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A lot of programs require you to pass sensitive information like passwords etc as arguments to the program. However if you pass passwords as arguments, it will be visible through the /proc filesystem or the ps ax output while the program is in execution. To avoid the possibility of anybody prying on sensitive information, programmers should modify the memory location where the input parameters are stored (argv array), so that it is not visible to any other users, who might have the access levels to see what processes you’re running. Jotted below is some sample code which modifies its input parameters to hide it from the proc file system.

#define      _GNU_SOURCE
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <string.h>

void main(int argc, char **argv) {
  char cmd[300];

  if (argc == 2) {
    int argvlen, i;
    printf("Unmodified argv[1] => %s\n", argv[1]);
    argvlen = strlen(argv[1]);
    for(i=0; i < argvlen; i++)
      argv[1][i] = 'x';
    printf("Modified argv[1] => %s\n", argv[1]);
    sprintf(cmd,"cat /proc/%d/cmdline", getpid());
    printf("/proc entry for the process at %s\n", cmd);
    system(cmd);
    printf("\nps ax entry for %s\n", argv[0]);
    sprintf(cmd,"ps %d", getpid());
    system(cmd);
  } else
    printf("Usage: %s some-string\n", argv[0]);
}

Sample output of the program.

@c $  ./modify_argv test
Unmodified argv[1] => test
Modified argv[1] => xxxx
/proc entry for the process at cat /proc/22493/cmdline
./modify_argvxxxx
ps ax entry for ./modify_argv
  PID TTY      STAT   TIME COMMAND
22493 pts/0    S+     0:00 ./modify_argv xxxx

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Here’s some sample C code which one can integrate into their projects to ping hosts. It uses fping instead of ping to do the actual pinging. Unlike ping, fping is meant to be used in scripts, so its output is designed to be easy to parse.

#define      _GNU_SOURCE
#include <stdio.h>
#include <arpa/inet.h>
#include <string.h>
#include <stdlib.h>

int
ping(char *ipaddr) {
  char *command = NULL;
  FILE *fp;
  int stat = 0;
  asprintf (&command, "%s %s -q 2>&1", "fping", ipaddr);
  fp = popen(command, "r");
  if (fp == NULL) {
    fprintf(stderr, "Failed to execute fping command\n");
    free(command);
    return -1;
  }
  stat = pclose(fp);
  free(command);
  return WEXITSTATUS(stat);
}

/*  Check if an ip address is valid */
int isValidIpAddress(char *ipaddr)
{
    struct sockaddr_in sa;
    int result = inet_pton(AF_INET, ipaddr, &(sa.sin_addr));
    return result != 0;
}

int main(int argc, char **argv) {
  int status = 0;
  if(argc != 2) {
    printf("Example Usage: %s 192.168.1.1\n", argv[0]);
    return 1;
  } else if(!isValidIpAddress(argv[1])) {
    printf("%s is an invalid IP Address\n", argv[1]);
    return 1;
  }
  status = ping(argv[1]);
  if (status) {
    printf("Could ping %s successfully, status %d\n", argv[1], status);
  } else {
    printf("Machine not reachable, status %d\n", status);
  }
  return status;
}

To install fping on ubuntu:

sudo apt-get install fping

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Kmscon is a simple terminal emulator based on linux kernel mode setting (KMS). It is an attempt to replace the in-kernel VT implementation with a userspace console. It is similar to the in-kernel terminal-emulator and is based on DRM. Listed below is the procedure to install kmscon in ubuntu.

sudo apt-get install libgles2-mesa-dev libgbm-dev libegl1-mesa-dev libdrm-dev libglib2.0-dev libfreetype6-dev
git clone https://github.com/dvdhrm/kmscon.git
./autogen.sh
make
sudo ./kmscon --switchvt

The last command will start kmscon on /dev/tty8.

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Assigning Google Adsense code to a PHP variable doesn’t work the way you would expect it to. I thought just deleting the newline characters and extra spaces from the adsense code and then assigning the resulting text to a variable should work. However it does not, and I’m not sure why. However what does work is shown below.

<?php
$googleadsensecode = '
<script type="text/javascript">
google_ad_client = "pub-123456789";
google_ad_slot = "123456";
google_ad_width = 300;
google_ad_height = 250;
//-->
</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>';
echo $googleadsensecode;
?>

The following example does not work.

<?php
$googleadsensecode = '<script type="text/javascript"> <!-- google_ad_client = "ca-pub-123456789"; google_ad_slot = "123456"; google_ad_width = 300; google_ad_height = 250; //--> </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script>';
echo $googleadsensecode
?>

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• Makefile – Check if a file exists using wildcard function: The following snippet of code can be used to check for … http://t.co/VSdW1QYj ->
• Yocto Project – Open Source Embedded Linux build system, package metadata and SDK generator.: The Yocto Project™… http://t.co/PwvVvbdv ->
• Configure Ubuntu to use Bash as default shell instead of Dash: Ubuntu uses Dash (Debian Almquist shell) as the def… http://t.co/JLXVzGS1 ->
• Going Beyond the Guidebooks – City Diary – TuoiTreNews http://t.co/fW4hHSVX ->
• Now is the worst time ever to buy an Android phone http://t.co/pGjIXz4E ->
• SCons: A software construction tool – Alternative to Make/Automake/Autoconf: SCons is an Open Source software cons… http://t.co/u4T2F7kb ->
• Usernoise modal feedback/contact form – #wordpress plugin – http://t.co/nkFmgvxb ->
• RT @tomosaigon: If you ever need to debug crazy bugs in Chrome, chrome://net-internals/ is AWESOME. Also: chrome://view-http-cache/ ->

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Foresight.js gives webpages the ability to tell if the user’s device is capable of viewing high-resolution images (such as the 3rd generation iPad) before the image is requested from the server. Additionally, it judges if the user’s device currently has a fast enough network connection for high-resolution images. Depending on device display and network connectivity, foresight.js will request the appropriate image for the webpage

• Request hi-res images according to device pixel ratio
• Estimates network connection speed prior to requesting an image
• Does not use device detection through user-agents
• Does not make multiple requests for the same image
• Javascript library and framework independent (ie: jQuery not required)
• Cross-browser and cross-platform
• Image dimensions set by percents will scale to the parent element’s available width and device pixel ratio
• Fully customizable through global configuration options and individual img attributes
• Default images will load without javascript enabled
• Minifies down to roughly 5K

foresight.js

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The longer way of executing multiple command with root permissions is to put all the commands into a script and then executing the script using sudo. However if you want to avoid doing that for something quick, the following command construct could be used.

sudo sh -c "whoami; whoami"

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The following snippet of code can be used to check for the existence of a file from within a Makefile.

ifneq ("$(wildcard $(PATH_TO_FILE))","")
FILE_EXISTS = 1
else
FILE_EXISTS = 0
endif

Quoting from make documentation.

In this present case, we are not using any wildcards, but the absolute path to the file.

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Javascript libraries for dealing with touch events, multitouch, normalizing across the Webkit/IE touch models

https://github.com/bebraw/jswiki/wiki/Touch

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