SYM

FFT(Fast Fourier Trasnform) howto by rookie

2014-07-07T00:00:00-07:00

FFT howto by rookie

7 July 2014 – Shanghai

Our team is working on a multimedia project for new Shanghai Natural Museum . One of the multimedia software was designed to simulate different kinds of animal sounds via mic and score it… I just wanna say: “Well done Buddy! Imagine the museum hall full of all kinds of strange wuuuuf ;)”

As expected, we are unable to find any developer willing to take this strange job. So I decided to try it myself.

Well, I admit I escaped from Math class in university just for playing CS. Don’t ask me how I managed to pass the exams:) But now I’m facing the consequence.

(To be continued…)

Dealing with args using getopt() [Part.2]

2014-07-04T00:00:00-07:00

Dealing with args using getopt() [Part.2]

4 July 2014 – Shanghai

In my previous post Dealing with args with getopt()[Part.1], I was very happy to find out a standard GNU library called getopt() which can help me out from the dirty job with commandline options.

Everything just work fine when you type in the options and arguments correctly. BUT the world is full of exceptions :( Below is my own commandline option setup:

Usage : soundView [-h] [-v volume] [-t Max_dB] [-f Floor_dB] filename

Let’s say I miss the volume argument after option -v, getopt won’t return ':' as promised. What actually happened is the next option -t was feeded as an argument for option -v, so the options after -v is totaly messed up! My code is tring to assign my variable: float volume = atof("-t") which always return 0.

Luckly I was able to get help from Stackoverflow . It’s a solution by manualy verify the optarg whether the first charator is "-" which solve my problem.

This is what my code piece finally looks like:

 1 //
 2 // Commandline argument processing
 3 //
 4 if(argc < 2){
 5     help();
 6     return 1;
 7 }
 8 
 9 // Setup default argument
10 paUserData.max_db = 80;
11 paUserData.floor_db = -180;
12 paUserData.volume = 0.2;
13 
14 int optionChar, prev_ind;
15 while(prev_ind = optind, (optionChar = getopt(argc,argv,"hv:t:f:"))!=EOF){
16     if(optind == prev_ind + 2 && *optarg == '-' && atof(optarg)==0){
17         optionChar = ':';
18         -- optind;
19     }
20     switch(optionChar){
21         case 'v':
22             paUserData.volume = atof(optarg);
23             cout << "Volume     :" << paUserData.volume << endl;
24             break;
25         case 'f':
26             paUserData.floor_db = atoi(optarg);
27             cout << "Floor dB   :" << paUserData.floor_db<< endl;
28             break;
29         case 't':
30             paUserData.max_db = atoi(optarg);
31             cout << "Max dB     :" << paUserData.max_db<< endl;
32             break;
33         case '?':
34         case ':':
35             cerr << "Argument error !" << endl;
36         case 'h':
37             help();
38             return 1;
39             break;
40     }
41 }
42 
43 char* fileName;
44 if(optind < argc){
45     fileName = argv[optind];
46 } else {
47     cout << "Sound file name must be specified." << endl;
48     return 1;
49 }

Still something to notice while reading the code above. First is the if statment

if(optind == prev_ind + 2 && *optarg == '-' && atof(optarg)==0){
    optionChar = ':';
    -- optind;
}

There are three conditions:

If current optind step 2 over previous means the current option is expecting argument.
the first charactor of the argument eq. “-”.
make sure it is not a negative number :)

While all conditions match, manually set returning optionChar to “:” and step optind back 1, so the following options won’t be messed up.

Another things to be noticed, the last args index left after processed by getopt is the filename we supplied. Currently pointed by optind, use argv[optind] to acquire it.

Dealing with args using getopt() [Part.1]

2014-07-03T00:00:00-07:00

Dealing with args using getopt() [Part.1]

3 July 2014 – Shanghai

Everyone start to learn coding by helloworld.c :) Yes, it’s the basic of digital daylife:
Command line

When dealing commandline style coding, every one need to manage the skill of controlling different kind of argument. It is really a dirty job by analyzing

int main(int argc, char *argv[])

But if you are familiar with POSIX style console command, you’ll find it’s argument definitions and help are so elegent and stylish.

Luckily we have a standard GNU C Library function called getopt

In short, we just need to add the include:

#include <getopt.h>

Then start coding with something like:

int c;
opterr = 0;
while ((c = getopt (argc, argv, "abc:")) != -1)
{
    switch (c)
    {
        case 'a':
            aflag = 1;
            break;
        case 'b':
            bflag = 1;
            break;
        case 'c':
            cvalue = atoi(optarg);
            break;
        case '?':
        case ':':
            if (optopt == 'c')
                fprintf (stderr, "Option -%c requires an argument.\n", optopt);
            else if (isprint (optopt))
                fprintf (stderr, "Unknown option `-%c'.\n", optopt);
            else
                fprintf (stderr, "Unknown option character `\\x%x'.\n",optopt);
            return 1;
        default:
            abort ();
    }
}

The third argument in funtion getopt defines the commandline option you need; single charactor means it is a switch with no extra argument is needed, on the other hand, if you need extra argument, put a ‘:’ after your option charactor.

Within the switch statment, you may notice the following case:

case ‘?’: If getopt finds an option character in argv that was not included in options, or a missing option argument, it returns ‘?’ and sets the external variable optopt to the actual option character.
case ‘:’: getopt returns ‘:’ instead of ‘?’ to indicate a missing option argument.

If you carefully read through the document, you will know the library will expose the following global variables:

optopt: When getopt encounters an unknown option character or an option with a missing required argument, it stores that option character in this variable. You can use this for providing your own diagnostic messages.
optind: This variable is set by getopt to the index of the next element of the argv array to be processed. Once getopt has found all of the option arguments, you can use this variable to determine where the remaining non-option arguments begin. The initial value of this variable is 1.
opterr: If the value of this variable is nonzero, then getopt prints an error message to the standard error stream if it encounters an unknown option character or an option with a missing required argument. This is the default behavior. If you set this variable to zero, getopt does not print any messages, but it still returns the character ? to indicate an error.
optarg: This variable is set by getopt to point at the value of the option argument, for those options that accept arguments.

Sounds like a beautiful story huh? But it do not have a happy ending.
I will discuss the matter and workaround in the next thread: Dealing with args using getopt() [Part.2]

Footstep of a rookie developer

2014-07-02T00:00:00-07:00

Footstep of a rookie developer

2 July 2014 – Shanghai

Well, just setup my first weblog on Github.

As a 34 years old man, I just decided to dive in the coding world.

Write the code, change the world

Yes it is. We are now in the middle of Information age, this time we can own the power to Make things by just sitting in front of a laptop and hit some strokes. I don’t think learning is such a pain. Having some basic knowledge of programming in high school, I was able to code something useful by googling:) AND THAT IS FUN! Check out some of my work at Github

So I setup a blog on github, just trying to record my steps on the road to a
developer.

Found a screenshot of my desktop... decade ago

2013-09-03T00:00:00-07:00

Found a screenshot of my desktop… decade ago

3 Sept 2013 – Shanghai

Organizing my old photos is such a funny things. Occasionally I found an very old screenshot of my desktop!

If looking at it carefully, you will find the brower is on the page of a famous local forum called KDS . And the post indecated the date is 2003 !

Yes, that time I just gratuated from SJTU and working at Shanghai TV Station as a CGer. Still a lot to learn: Maya, Shake, Mel develop etc. And I am the only one in our group working on a station running Linux desktop! That’s a * Redhat 9 * with KDE.

Compare to the desktop environment now-a-days, it still look so elegent and effecient. My favorate linux distro. is Debian with FVWM2 desktop.

How many 10 years do we still have?