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In reading the man pages for tcpdump, I saw that the -dd arguement would output the dump as a fragment of a C file. In what situations is that useful? I take it this is to quickly include and compile the fragment in a program that will be used to process the data according to code we write ourselves? Does this have its utility with unknown or new protocols? Is there some other common, standing situation in which this is needed? Just curious.
It's useful if you're writing a program using libpcap/WinPcap that would use a filter but that, for whatever reason, wouldn't run pcap_compile() to translate a filter string into BPF machine code; it lets you do the compilation with tcpdump and generate some text that you could use in the initialization of an array of struct bpf_insn (a pointer to which, and a count of elements in which, you'd put in a struct bpf_program).
I'm not sure who would do that, however.
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I have been learning c and data structures for quite some time now and I wanted to see whether I could apply what I have learnt. I searched a bit and found out that I could start with util linux but, before I could do so, I thought I'd check and perhaps dabble a bit with the code for basic unix commands like "cat". I was able to understand what a part of the code might have been trying to do, but I was not able to understand the entire code as a unit.
For example, in the "cat" code, a pointer to the output buffer and input buffer is declared and is appropriately used, which I could understand. What i could not understand, are parts of code like io_blksize (stat_buf) which has no description whatsoever, on what it does. Or how two pointers declared as pointers to the input and output buffers, actually correspond to the input and output buffers ?
So my question being, how do I approach these type of code, how can I understand something that has no description to what it does (in the example given above) and how can I make and implement changes in the code, so that I can see the changes when i run a command ?
(Would really appreciate references or topics I should start with, so that I can relate what I have learnt to how command code's can be modified. I also apologize if the question is to abstract.)
This is a bit of a subjective question so my answers will just be my opinion of course.
A good place to start when you run into something you don't recognise while reading source code is the manpages. Each function will generally have a manpage, e.g. man 2 read or man 3 printf. Beyond that, I feel perhaps you should get more of a foundation in Unix before attempting to read the straight source code, a good book is Advanced Programming in the Unix Environment. I've been working through it myself and am finding my Unix knowledge improving considerably.
Just my two cents.
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I want to write a program that formats a disc to a new format (not NTFS or FAT32) and can read from and write to the disc, In order to do this, I have to have a way to write single bytes to a disc (without creating files). How do I do that?
EDIT: I found this. But I'm not sure if using CreateFile() as Eli Bendersky said in the first answer (when organized in order of votes) let's you write one byte (or even one bit) at a time, or do you have to write full sectors at a time.
Answer: Since I can't post an answer the question because it was closed, I will answer it write here. You don't need need API functions to do this. All you need to do is open the disk like you open any other file. Like this:
int hFile;
hFile=open("/dev/sdb",0_RDWR);
You program has to directly talk to the driver as you will be by-passing the file-system.
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I am bit new to programming and i want to send a float data to eeprom from a controller and i want to implement crc for the error detection of the data when ever i tries to read or write.
This is my intention.But i found many algorithms for implementing crc and its been quite confusing for me to follow which one.
The compiler provides 4 bytes of space for all data and its function sends each byte one at a time.So i trust i would be required to do the crc of each 8bit data or can implement it as a whole.
And i am using C language.
In brief:
i just need to do a
1.Crc implementation.
2.Common Data size =32 bits
3.Compiler function sends one byte at a time.
4.And how do we fix which algorithm to go for.
Thank you very much
Try Reading this article(It Contains C Codes and Diagrams Which you need) :
http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
CRCs are among the best checksums available to detect and/or correct errors in communications transmissions. Unfortunately, the modulo-2 arithmetic used to compute CRCs doesn't map easily into software. This article shows how to implement an efficient CRC in C.
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I would like to know if it is possible to port GNU grep as a libary, leaving aside the legal complications, if any, as this is purely for non-commercial, but academic use. I have seen many ports exist of GNU grep. For example : GNU grep for win 32 here.
I wonder why nobody has ever attempted to port grep as a library ? It would be a huge benefit to applications that exploit string searching/mining as they can use the power of GNU grep internally in the their applications. I would like to attempt this feat, but since I am new to string searching/mining, would love to know the obvious challenges that may arise and why it has not been done as yet.
EDIT - The advantage of a GNU grep library is that it will do string searching much faster, using its own modified version of boyer-moore. Where as when using a regular expression wrapper library such as PCRE or Boost reg exp or Qt Reg expressions etc, the application has to read the file line-by-line and parse each line against the regexp. This is the obvious advantage that I see.
Yes. Just link it as a library and call its main() with its intended arguments. Or better if you rename its main() to some better, f.e. to grep().
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My anti-virus identifies the compiled ".exe" of this source as a virus
"Gen: Variant:Graftor" . Can anybody explain why?
void main()
{
float x=3.0/7.0;
double y=3.0/7.0;
int a= (x==y);
}
Well, unmanaged / native programs can pose security risks and probably your antivirus marked this as such. Antiviruses use heuristics - so the algorithms are aproximate, they tend to work on a "best effort" idea, and in case of antiviruses "false positives" like your sample is preferable to missing actual viruses.
Another possibility is the way you compiled your program, there are a lot of compiler optimization and some are related to security - so your program randomizes certain parts of the memory etc. Maybe the antivirus looks at how a C program is compiled and yours has no security flags turned on? Hmm...
About Generic Detections
Unlike more traditional detections (also known as signatures or single-file detections) a Generic Detection does not identify a unique or individual malicious program. Instead, a Generic Detection looks for broadly applicable code or behavior characteristics that indicate a file as potentially malicious, so that a single Generic Detection can efficiently identify dozens, or even hundreds of malware.
This is a false positive. These sometimes occur in every antivirus product because of the complexity of present-day malware and file compression/protection utilities that are used on both malware and legitimate software.