Sleepless Nights When Coding

A computer engineer's coding blog. What a surprise!

[sleeplesscoder]

Stdout Buffer

After a long time, I decided to post again since I needed just one small information; however, it took some of my time. The information is not about C, but unix shell.

I was running a Python script, which just checks the status of some URLs and prints their index or any error if exists. Since the number of URLs was large, I wanted to see the progress on the console. Additionally, I needed to know erroneous URLs if any. However, I didn’t do that saving/logging in Python. I wanted to handle it in the terminal.

In order to print to the terminal and a file at the same time, I have used Tee:

./script.py | tee output.txt

In the above line, the output of script is piped (redirecting output one program to another) to tee, which prints to stdout (the console (actually, the file descriptor for non-error output) and the file output.txt at the same time. Additionally, I combined stderr (the file descriptor for error output) with stdout in the following line:

./script.py 2>&1 | tee output.txt

1 and 2, respectively, represent stderr and stdout.  2>&1 combines stderr with stdout.

After typing the last command, it should have worked. However, I couldn’t see any output in the terminal. Then, I learned from the Internet that it is due to the buffer. So that I know the reason, how I can force buffer of stdout not to keep anything? I found the answer again online:

stdbuf -o 0 ./script.py 2>&1 | tee output.txt

stdbuf is a command, which can set the buffer settings of stdin (input stream), stdout, and stderr. With the parameter -o, I set the buffer size of stdout to 0 when I’m running the script. Then, the output of the script appeared on the terminal without any delay.

On some websites (including the first answer of the reference), it is mentioned that unbuffer from the package expect is suggested to stop buffering. However, I do not think that it is necessary to install another tool for such a one-line thing.

References:

http://stackoverflow.com/a/11337109/1080580

[sleeplesscoder]

C Header tip

Header files from the C standard library headername.h     when used in C programs cheadername      when used in C++ programs (note the c as a prefix). For instance, to include the stdlib header file in a C program        #include <stdlib.h> in a C++ program    #include <cstdlib> References: http://www.cprogramming.com/function.html?sb=prop Date & time when I wrote this note: 31.12.2011 04:17

[sleeplesscoder]

Pointer Tip 2

#include <stdlib.h> int *ptr = malloc( sizeof(int) ); This code set ptr to point to a memory address of size int. The memory that is pointed to becomes unavailable to other programs. This means that the careful coder should free this memory at the end of its usage lest the memory be lost to the operating system for the duration of the program (this is often called a memory leak because the program is not keeping track of all of its memory). The free function returns memory to the operating system. free( ptr ); After freeing a pointer, it is a good idea to reset it to point to 0. When 0 is assigned to a pointer, the pointer becomes a null pointer, in other words, it points to nothing. By doing this, when you do something foolish with the pointer (it happens a lot, even with experienced programmers), you find out immediately instead of later, when you have done considerable damage. The concept of the null pointer is frequently used as a way of indicating a problem--for instance, malloc returns 0 when it cannot correctly allocate memory. You want to be sure to handle this correctly--sometimes your operating system might actually run out of memory and give you this value! References: http://www.cprogramming.com/tutorial/c/lesson6.html Date & time when I wrote this note: 31.12.2011 03:34

[sleeplesscoder]

Pointer Tip

int x;            int *p;           p = &x;           scanf( "%d", &x ); is equivalent to scanf( "%d", p ); since scanf takes the memory address as the second argument. printf( "%d", x ); is equivalent to printf( "%d", *p ); since *p is x. References: There is no source, just I wondered. Date & time when I wrote this note: 31.12.2011 03:22

[sleeplesscoder]

Writing Hex and Octal Values in C

In C/C++/Java, hex numbers begin with 0x. Octal numbers begin with 0. 023 is 238 (which is 19 in base 10). 0x23 is 2316 (which is 35 in base 10). int x = 0x23 ; int x = 35 ; To a computer, assigning 0x23 to x and assigning 35 to x is the same. Both get saved to the same 2C value. It doesn't matter than in the source code, that it was assigned as 0x23 or 35. That matters only to the compiler. The compiler must recognize that 0x23 is hexadecimal, and convert it appropriately to 2C. Or it must recognize that it is 35, and again convert it to 2C. Either way, once it is in executable format, there's no information about how it got there. That information only resides in the source code. How to Write a Negative Value: -0x23 = -35 I think, 2C represents 2's complement (related to the binary representation). For detailed information: http://en.wikipedia.org/wiki/Two%27s_complement The format specifier of a hexadecimal number: X (outputs capital letters) or x Ex:     printf("%X %x %d\n",0xA2,0xA2,0xA2); outputs A2 a2 162 References: http://www.cs.umd.edu/class/sum2003/cmsc311/Notes/BitOp/hexoctal.html http://www.cplusplus.com/reference/clibrary/cstdio/printf/ Date & time when I wrote this note: 31.12.2011 03:16

[sleeplesscoder]

Merhaba Dünya!

Hello everyone!

This is the very first entry of this blog. Like most programming stuff, this blog starts with a "Hello World!"(the title) too, except that it is in Turkish.

As you may guess, I live in Turkey. I study computer engineering in Istanbul.

The first time I've learnt something about coding is 2004, but I was not really into it. That year I learnt some VB 6.0 syntax and implemented very simple programs. In the next 5-6 years I learnt only a bit of HTML and not anything else (I don't know why). I learnt serious coding stuff one and a half year ago in my university. I actually enjoyed programming that time and my actual coding life started with Java. Then I started to code with some other languages (C, C++, PHP etc.). I'm still interested in them.

I decided blogging about coding when I read this post. It really inspired me. I had to create a blog primarily to share some computer/programming tips. Unfortunately, I postponed blogging for a while, however I kept these notes on my computer. So, I share them now and I will continue to post new stuff!

Again, hello world!

(Note: I will post these things also in turkish here: http://uykusuzkodcu.blogspot.com/)