C++ replace data in binary file with fstream
I try to replace data in binary file using C++ and fstream library. Is it possible to do that with this library?
I would like to change one byte of file in address: 0xB07 to 1.
I have written the following code snippet:
...
int address = 0xB07;
char * toChange = new char('0');
std::ifstream input(filename, std::ios::binary);
input.seekg(address);
input.read(toChange, 1);
input.close();
*toChange = (char)0x01;
std::ofstream output(filename, std::ios::binary);
output.seekp(address);
output.write(toChange, 1);
output.close();
...
I have tried many versions of this code and I still can't understand why the byte doesn't change.
c++ fstream binaryfiles istream
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
add a comment |
I try to replace data in binary file using C++ and fstream library. Is it possible to do that with this library?
I would like to change one byte of file in address: 0xB07 to 1.
I have written the following code snippet:
...
int address = 0xB07;
char * toChange = new char('0');
std::ifstream input(filename, std::ios::binary);
input.seekg(address);
input.read(toChange, 1);
input.close();
*toChange = (char)0x01;
std::ofstream output(filename, std::ios::binary);
output.seekp(address);
output.write(toChange, 1);
output.close();
...
I have tried many versions of this code and I still can't understand why the byte doesn't change.
c++ fstream binaryfiles istream
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03
add a comment |
I try to replace data in binary file using C++ and fstream library. Is it possible to do that with this library?
I would like to change one byte of file in address: 0xB07 to 1.
I have written the following code snippet:
...
int address = 0xB07;
char * toChange = new char('0');
std::ifstream input(filename, std::ios::binary);
input.seekg(address);
input.read(toChange, 1);
input.close();
*toChange = (char)0x01;
std::ofstream output(filename, std::ios::binary);
output.seekp(address);
output.write(toChange, 1);
output.close();
...
I have tried many versions of this code and I still can't understand why the byte doesn't change.
c++ fstream binaryfiles istream
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
I try to replace data in binary file using C++ and fstream library. Is it possible to do that with this library?
I would like to change one byte of file in address: 0xB07 to 1.
I have written the following code snippet:
...
int address = 0xB07;
char * toChange = new char('0');
std::ifstream input(filename, std::ios::binary);
input.seekg(address);
input.read(toChange, 1);
input.close();
*toChange = (char)0x01;
std::ofstream output(filename, std::ios::binary);
output.seekp(address);
output.write(toChange, 1);
output.close();
...
I have tried many versions of this code and I still can't understand why the byte doesn't change.
c++ fstream binaryfiles istream
c++ fstream binaryfiles istream
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
edited Nov 21 '18 at 14:51
happysadek
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
asked Nov 21 '18 at 14:03
happysadekhappysadek
13
13
As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03
add a comment |
As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03
As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03
add a comment |
1 Answer
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This code will remove your file and put totally new contents in it.
The problem is in line
std::ofstream output(filename, std::ios::binary);
That's because the default open mode is ios::out | ios::trunc (See for ex.: Input/Output with files)
Which means file is being truncated to zero bytes.
Then your seek() function extends him to the specified size (usually filling with zeroes) and finally output.write() writes the byte at the end.
In order to do what you want I had to specify the following ofstream flags: std::ios::binary|std::ios::out|std::ios::in
I cannot say currently for sure why the std::ios::inis needed, sorry...
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
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active
oldest
votes
This code will remove your file and put totally new contents in it.
The problem is in line
std::ofstream output(filename, std::ios::binary);
That's because the default open mode is ios::out | ios::trunc (See for ex.: Input/Output with files)
Which means file is being truncated to zero bytes.
Then your seek() function extends him to the specified size (usually filling with zeroes) and finally output.write() writes the byte at the end.
In order to do what you want I had to specify the following ofstream flags: std::ios::binary|std::ios::out|std::ios::in
I cannot say currently for sure why the std::ios::inis needed, sorry...
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
add a comment |
This code will remove your file and put totally new contents in it.
The problem is in line
std::ofstream output(filename, std::ios::binary);
That's because the default open mode is ios::out | ios::trunc (See for ex.: Input/Output with files)
Which means file is being truncated to zero bytes.
Then your seek() function extends him to the specified size (usually filling with zeroes) and finally output.write() writes the byte at the end.
In order to do what you want I had to specify the following ofstream flags: std::ios::binary|std::ios::out|std::ios::in
I cannot say currently for sure why the std::ios::inis needed, sorry...
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
add a comment |
This code will remove your file and put totally new contents in it.
The problem is in line
std::ofstream output(filename, std::ios::binary);
That's because the default open mode is ios::out | ios::trunc (See for ex.: Input/Output with files)
Which means file is being truncated to zero bytes.
Then your seek() function extends him to the specified size (usually filling with zeroes) and finally output.write() writes the byte at the end.
In order to do what you want I had to specify the following ofstream flags: std::ios::binary|std::ios::out|std::ios::in
I cannot say currently for sure why the std::ios::inis needed, sorry...
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
This code will remove your file and put totally new contents in it.
The problem is in line
std::ofstream output(filename, std::ios::binary);
That's because the default open mode is ios::out | ios::trunc (See for ex.: Input/Output with files)
Which means file is being truncated to zero bytes.
Then your seek() function extends him to the specified size (usually filling with zeroes) and finally output.write() writes the byte at the end.
In order to do what you want I had to specify the following ofstream flags: std::ios::binary|std::ios::out|std::ios::in
I cannot say currently for sure why the std::ios::inis needed, sorry...
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
answered Nov 22 '18 at 9:52
LiMarLiMar
1,49621522
1,49621522
add a comment |
add a comment |
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As you have not provided a Minimal, Complete, and Verifiable example that we could try for ourselves, we are limited to your description. So what does "it doesn't work" mean? Do you get some error message? Something unexpected happens? (what is it?)
– jakub_d
Nov 21 '18 at 14:33
Sorry for that. 'It doesn't work' means that the bytes aren't replaced. I can check them for example in Hex Editor.
– happysadek
Nov 21 '18 at 14:40
Try adding error checking to the write part. Maybe the file is not actually writable? At least it would tell you which part is failing.
– jakub_d
Nov 21 '18 at 14:45
I hope my question is better now. How to add error checking? I have tried to check output.bad() but it returns false.
– happysadek
Nov 21 '18 at 15:00
Can an ofstream constructor fail? How does it indicate failure? Check for it. Can seekp fail? How does it... (etc.) To answer the Hows, look at the reference cplusplus.com/reference/fstream/ofstream
– jakub_d
Nov 21 '18 at 15:03