humble iron
I have this file, and you can see the values in the hex dump.
I have looked at how to use ifstream, but I think that will read it as characters instead of values.
I want to read the values as decimal, and store it into a array. after that I think I can manage.
humble iron
the data is the mnist database of handwritten images. so the numbers written are 1 pixel, and range from 0 to 255
zealous mulch
I have this file, and you can see the values in the hex dump.
I have looked at ...
your hex view shows a long sequence of bytes, each byte from 0 to 255
use ifstream, read the chars, and use them
zealous mulch
decrypting the bytes and parsing them into numbers with a neural network that is trained on hand draw images of numbers, well that's on you
humble iron
use ifstream, read the chars, and use them
its actually not chars, but rather unsigned 1 byte. so from 0 to 255.
you can see the chars side is gibberish
so I want to read the stream and fill it in a array
humble iron
use ifstream, read the chars, and use them
oh ok its a char because its one byte 👍
humble iron
I have been able to successfully read the values from the file.
however there is a small prob.
when, I run this, i prints as 46831335. however in the hex editor, I can see there are 47040000 bytes. so where did the remaining bytes go?
zealous mulch
when, I run this, i prints as 46831335. however in the hex editor, I can see the...
when running in text mode, operator>> skips whitespace chars (\n ascii code 10, ' ' ascii code 32, and so on) and, \r (ascii code 13) gets completely skipped in MS Windows, thus corrupting your pixels
open ifstream in binary mode
and use the function read
to extract bytes in your pixel, or your local fixed length array
humble iron
to extract bytes in your pixel, or your local fixed length array
the problem is that the read function doesnt accept unsigned char values.
file.read(char*, int)
zealous mulch
the problem is that the read function doesnt accept unsigned char values.
`file....
no, it does
pass a pointer
humble iron
here I cant have unsigned char pixel, instead of char pixel
zealous mulch
here I cant have unsigned char pixel, instead of char pixel
use reinterpret_cast<char*>(&pixel)
humble iron
use `reinterpret_cast<char*>(&pixel)`
btw, what is this?
zealous mulch
btw, what is this?
"grab the piece of memory where unsigned char pixel lives and pretend that a char lives there"
this is how you read bytes into variables
humble iron
!solved
raw meteorBOT
zealous mulch
!solved
calling read and reading 1 char is not very optimal, consider reading larger chunks to improve performance
ifstream underneath tries to read in chunks, load them in memory and give you chars one by one from there, but that's a call to read every single time
also, your calling of close() is redundant, ifstream has a destructor which will call close for you
don't be a C dev, be a C++ dev 🙂
humble iron
ifstream underneath tries to read in chunks, load them in memory and give you ch...
should I do
fresh dew
char pixels[47040000]
file.read(pixels, 47040000)
?
zealous mulch
should I do
```cpp
char pixels[47040000]
file.read(pixels, 47040000)
```
?
you are forgetting, the ammount of space for local variables is ~2MB, your program will explode before main starts
allocate memory from the heap first, then run your read
zealous mulch
`static char pixels[47040000]` ?
this will bloat your executable to be as large as this array in bytes, plz dont
humble iron
first day