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- Error in reading a byte from a file.
Error in reading a byte from a file.
Hello,
I am trying to read bytes from a file but it's just not working...
My program reads graphic data from a file and then creates a png image.
If i manually specify the coordinates instead of reading them from a file it works fine.
However reading the byte from the file does not work.
Any ideas?
Thanks in advance.
For example.
This works...
But this does not.
I am trying to read bytes from a file but it's just not working...
My program reads graphic data from a file and then creates a png image.
If i manually specify the coordinates instead of reading them from a file it works fine.
However reading the byte from the file does not work.
Any ideas?
Thanks in advance.
For example.
This works...
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But this does not.
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Last edited on
First thing is to check that your file is being opened correctly.
After line 7:
seekg's second parameter is an enum. You should use ios::beg instead of 1.
How do you know this magic number is correct?
After line 7:
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seekg's second parameter is an enum. You should use ios::beg instead of 1.
| 0x2B6D78 |
Last edited on
Thanks for your reply.
I inserted that and it doesn't throw an error.
that number is an address in my file. I know it's correct as i checked in a Hex viewer.
I inserted that and it doesn't throw an error.
that number is an address in my file. I know it's correct as i checked in a Hex viewer.
To reiterate, your code does not compile on a modern compiler.
On my compiler, std::ios::beg is 0, not 1.
Are you absolutely positive that ios::beg is 1 on your system? It's implementation-defined, which is why the enum should be used.
https://en.cppreference.com/w/cpp/io/ios_base/seekdir
You may also want to consider doing other sanity check tests, for example, reading the second byte of the file:
Check that it matches what your hex viewer shows.
Edit: ios::cur would also work for your code... which does happen to have a value of 1 on my compiler. So perhaps that part of your code is not the issue, but you should be using the ios enums.
main.cpp: In function 'int main()':
main.cpp:8:20: error: invalid conversion from 'int' to 'std::ios_base::seekdir {aka std::_Ios_Seekdir}' [-fpermissive]
inFileK.seekg(0x2B6D78, 1); // Location of the header. |
On my compiler, std::ios::beg is 0, not 1.
Are you absolutely positive that ios::beg is 1 on your system? It's implementation-defined, which is why the enum should be used.
https://en.cppreference.com/w/cpp/io/ios_base/seekdir
inFileK.seekg(0x2B6D78, ios::beg); // Location of the header. You may also want to consider doing other sanity check tests, for example, reading the second byte of the file:
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Check that it matches what your hex viewer shows.
Edit: ios::cur would also work for your code... which does happen to have a value of 1 on my compiler. So perhaps that part of your code is not the issue, but you should be using the ios enums.
Last edited on
Does 'endiness' have to be considered here?
What values are you getting for oDataK[13] and oDataK[14]. If not as expected (0x7c, 0x7e), where do these consecutive values occur in the data file using the hex viewer (is this configured properly)?
What values are you getting for oDataK[13] and oDataK[14]. If not as expected (0x7c, 0x7e), where do these consecutive values occur in the data file using the hex viewer (is this configured properly)?
Last edited on
Here is a screenshot of my Hex editor. They are highlighted in yellow.
https://i.imgur.com/0sUA4Ds.png
I am trying to read these 2 bytes individually. X and Y.
https://i.imgur.com/0sUA4Ds.png
I am trying to read these 2 bytes individually. X and Y.
From the picture, the address of the yellow bytes is 0x2B6D84 which is only 12 10 (not 13) bytes from the start of the header at 0x2B6D78
Last edited on
A little debugging may point out something obvious. Specifically, I'm unconvinced that your method of reading in the file and going through the char array is actually doing the equivalent of your first code:
If x_coord and y_coord are different values, the issue has to come from the way you're parsing the file. I recommend outputting the values, seeing where the come from within the file, and seeing if there's a margin of error in where you thought the values were vs where you ended up.
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If x_coord and y_coord are different values, the issue has to come from the way you're parsing the file. I recommend outputting the values, seeing where the come from within the file, and seeing if there's a margin of error in where you thought the values were vs where you ended up.
If you are seeking to 0x2B6D78, then x_coord (0x7c) is offset 10 and y-coord (0x7E) is offset 11.
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Location off val 0x2B6D78 00 0x01 0x2B6D79 01 0x02 0x2B6D7A 02 0x02 0x2B6D7B 03 0x00 0x2B6D7C 04 0x00 0x2B6D7D 05 0x04 0x2B6D7E 06 0x10 0x2B6D7F 07 0x02 0x2B6D80 08 0x78 0x2B6D81 09 0x6E 0x2B6D82 10 0x7C 0x2B6D83 11 0x7E |
Last edited on
So I have it partially figured out.
However I am Having an issue were the previous blocks of code don't work when I add an if statement after the previous block.
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Last edited on
You should try stepping through your code line by line with a debugger so you can tell in exactly what way it is going wrong.
Not sure what I did but its working now. It might have been to do with conflicting ifstream's or in the wrong location in the code?
Thanks!
Thanks!
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