Saving bytes of int in binary file

Question

Hi!
I have 38 digits long int. And i wants to save that integer in a BINARY file using C program.
I use "putw" function to store int to file. This function works well with small int but it is overflowing with 38 digits long int.

As we know that storing very long digits is not any problem in PYTHON.
I'm using this in PYTHON to store int in BINARY file:
file.write((very_long_int).to_bytes(16, byteorder="small", signed=False))
And in C I'm using putw(very_long_int, file)
The problem in C is that not any data type can store that large number.

Can anyone help me ??
Please.

Answer 1

🌀 Shail Murtaza شعیل مرتضیٰ wrote: "Flash
If this discussion was that simple then you really think that it will be that long ??"

I don't know well C, but I don't think your problem is quite difficult by itself... I believe that your question is too unclear, and that's the primarly cause of the numerous posts here, not the problem itself ^^

what is exactly your problem?

title seems to talk about only writting bytes in files, while description suggest you're rather stuck at converting your big number string / digits array to big endian order...

in former case, the first Flash answer would be enough to solve it because he's iterating an array to write bytes instead of char in a file (opened in binary rather than in text mode produce issue by stopping writting when a null byte is encountered), even if he doesn't convert your big number to big endian bytes...

[post char limit reached: to be continued]

Answer 2

Coder Kitten
Thanks!
I'm currently using ghex to read file

Answer 3

Coder Kitten
Now I'm trying to write file using
fputs("\x62\x04\x00\x00");

62 4 are written to file but I'm unable to write those last two zeros.

Can you help me in this

Edit:
I was able to do that using fputc
I guess \x00 was representing null character, that's why fputs wasn't working.
😃😃😃

Answer 4

you could try these files. beware they won’t run on SoloLearn as they expect cmd args. the C file reads a ‘big’ int data and writes in a binary file (.bin for example). the PY file reads the binary file and displays the integer representation of that data. the input num of C file and output of PY should be identical. Minimal error check is done and I tested on a Linux machine. hope this gives some ideas.

https://code.sololearn.com/c4A204A13a0a/?ref=app

https://code.sololearn.com/ca13A4A6A7A0/?ref=app

Answer 5

🌀 Shail Murtaza شعیل مرتضیٰ, actually binary number system is similar to decimal: just different base (2 instead of 10).
1122 in binary is 10001100010. If divide into bytes, then we get 100 01100010 = 00000100 01100010. In hexadecimal it will be 462 = 04 62.
And, I think, Flash gave Python code because Python lets the number be as long as needed.

Answer 6

get
I was saying to flash that his program is not actually saving int in file but characters like 1,2,3,4.
I already know that characters are represented by int in C.
I hope that you will understand.
This is hard for me to explain

Answer 7

[answer 2nd part]

in last case, the problem is not as hard as it could seems, as I am able to convert 38 digits decimal int string to bytes (hex) by spending some minutes to the logic and some hours to get the skills needed to implement it ;P

anyway, I will not post it now, without knowing if that's the answer you're looking for, as your numerous figthing posts with Flash doesn't make us want trying to help without first asking for clarification ^^

Answer 8

🌀 Shail Murtaza شعیل مرتضیٰ as you do also...

why doesn't matter...
you're already posted two posts to claim your rights, but doesn't try to clarify your question or even answer my doubt about what you're asking: I will keep my code private, and pass to something else so ^^

Answer 9

Coder Kitten
It is not.
I'm just giving directly argument to putw function.
But it's overflowing.

Answer 10

Coder Kitten
I can save each digit individualy in array.

But problem is that how I can save that number in BINARY file.

Because putw function first convert number in hex form and then save it.

Answer 11

Coder Kitten
As array of integers

Answer 12

Coder Kitten

I'm trying to modify a BINARY file.
I can't store numbers directly in it like
16
First I need to convert that number to bytes i.e.,
\x00\x10

Answer 13

Coder Kitten

I doesn't know much about these things.

I just want to save integer in a file.
For example if I will save "1122" in file then file will have

"62 04 00 00"

I can save small integers but can't large.

Answer 14

Flash
Thanks for help.
😄😄😄
But this is not what I want.

Your program is just writing characters in file not integer. This is very easy.

Answer 15

🌀 Shail Murtaza شعیل مرتضیٰ I think you should check. it writes bytes, not characters. besides C can’t have that long int in any integral datatype. I also posted a PY file. you can verify there if its a character or byte.

Answer 16

Flash
You're just reading characters from file and converting them to integer using PYTHON. Which is also too easy.

Answer 17

no point in arguing if you don’t get the basics right. anyway. nevermind

Answer 18

Flash
You really don't know about BINARY, do you.
if you want to save 1122 in your file then hex representation of that binary will be
0x62 0x04 0x00 0x00

Answer 19

Flash
When you will save int to file then series of hexadecimal numbers will represent one integer.

When you will save character then one hexadecimal number will represent one character.

If I will save 1234 with your program then I will get
31 32 33 34 as hex in file
each number is individual

Answer 20

🌀 Shail Murtaza شعیل مرتضیٰ,
1. Character (as <char> date type in C and C++) is actually just a 8-bit integer, and compilers just give it special behaviour when inputting and outputting, not like other integer data types (<int>, <long int>, <short int>, <unsigned int>, etc.).
2. It will be the same effect. Binary is just a series of 0's and 1's, as decimal also includes 3's, 4's, ... upto 9's. And it is up to the programmer how the program will process this binary data.