Compressing a raw file

[Prasannaprabhus]

I had written a c code that can compress a raw file where my requirement is, There should not exist continual repetitions of 3 bytes in a raw file where I have to compress it and decompress it.
Ex: aaaaaabbbbbbccccccccccccbbbbbbbbbbbb is raw input
encoded file should be aaa2bbb2ccc4bbb4 and on decoding I should get same file as it was before. code for compress and decompress is attached.Its working for text file please some one help me the same for Raw file.

[donbock]

What if the original file was "aaa2bbb2ccc4bbb4" -- how will you determine that decompression is not needed in this case but it is needed in your original example?

[Prasannaprabhus]

Thank you for the quick response.And my given file is a raw file and its enough if it gets compressed.Whatever may be the pattern my end application is concentrated on just compressing and decompressing given raw file in above mentioned format

[donbock]

Did you invent this compression/decompression algorithm or was it specified for you?

Your original post gave an example of a text file, both original and compressed. Please give a similar example of what you expect for a raw file.

[Prasannaprabhus]

Actually I took example to make sure one understand what has to be done and criteria.and ya seeing the requirement I decided this would be most probably the suitable one.And my actual criteria is just read 3 bytes from a raw file and see that the 3 bytes pattern won't repeat continually. Ex .R24 format file. For text file the same one which I ve attached would work. But for raw data file some readings are not getting proper so thought if a post some one would help.

[Prasannaprabhus]

Please some one throw light towards it.If at all any changes to be considered while editing or reading a raw file do inform.

[donbock]

I assume you mean "binary file" when you say "raw file".
I don't understand your compression algorithm. Please indicate the desired encoded file for the following 12-byte unencoded binary file:
0x01 0x01 0x01 0x01 0x01 0x03 0x03 0x04 0x04 0x04 0x05 0x06

[Prasannaprabhus]

What ever pattern consider 3 bytes should not repeat ex:abcabcabc021369/*-/*-****** to be encoded as abc030210136901/*-02***02
(Given I ve considerd ex of this only to understand the encoded format.In actual file all characters in extended ascii)

[Prasannaprabhus]

♀A╘b╝╝╝.₧B╝▐▐▐▐▐▐▐*╧****■■■■■■■■■■^■■■■ this is how the content look like in the given raw file

[donbock]

I'm afraid I don't understand how this compression algorithm works. So I'll just give you some general comments on your code...

encoding.txt

• Should the output file be opened as a binary file?
• You don't check if fread returns a value smaller than 3.
• You use strcpy and strcmp, but a binary file might contain a data value of zero, which would be mistaken for a terminating null.
• Near the bottom is "if(ctr <= f)". Where is f defined?
• Right after that is "fprintf(tfp,"%x",0);" This puts a binary zero (not '0') in the file. Is that what you want to do?
• At the top of your loop you use fwrite, at the bottom you use fprintf. Shouldn't they all be fwrite?

deoding.txt

• Probably should open both files for binary access.
• You should check if fread returned fewer characters than you asked for.
• This function expects the repetition count to be two decimal-ASCII characters. I see nothing in encoding.txt to prevent the count from being more than two characters.