R
rusttree
I'm working on a program that manipulates bmp files. I know the offset
location of each piece of relevent data within the bmp file. For
example, I know the 18th through 21st byte is an integer value
representing the width of the bmp image. So far, I have been able to
use fstream's seek, write, and read to pull out chucks of bytes and
convert them to usable integers straight out of the binary file. It
works well, but over the course of my program there are thousands of
writes and reads, which I imagine is not the most efficient way of
processing the data.
Instead, I want to read in the entire bmp binary data into one
character string, say "buffer". I want to then pick out 4-byte chunks
of buffer and convert them to usable integers, do all of the necessary
processing, then write the whole buffer back to a new bmp file. This
would require only one write and one read. My experience with binary
character manipulation is, however, very limited and I have not yet
been able to pick out the individual bytes from buffer that I want.
Here's an example of how I'm trying it:
<******>
char buffer[25000000]; //buffer can handle a bmp up to 25MB
int fileSize;
int width;
ifstream bmp ("image.bmp", ios::binary); //open bmp for binary input
bmp.seekg(0, ios::end); //put cursor at end of file
fileSize = bmp.tellg(); //offset of last byte = size of file
bmp.seekg (0, ios::beg); //put cursor at beginning of file
bmp.read (buffer, fileSize); //read entire bmp into char string buffer
width = (int)buffer[18];
cout << width << endl;
<******>
Instead of setting the 18th, 19th, 20th, and 21st byte into "width", it
just sets the 18th byte by itself. I was hoping c++ would be smart
enough to realize that since "int width" was 4 bytes by definition, it
would know to fill in the other 3 appropriately. So my question is how
would I get all 4 bytes into "width" as an integer value.
location of each piece of relevent data within the bmp file. For
example, I know the 18th through 21st byte is an integer value
representing the width of the bmp image. So far, I have been able to
use fstream's seek, write, and read to pull out chucks of bytes and
convert them to usable integers straight out of the binary file. It
works well, but over the course of my program there are thousands of
writes and reads, which I imagine is not the most efficient way of
processing the data.
Instead, I want to read in the entire bmp binary data into one
character string, say "buffer". I want to then pick out 4-byte chunks
of buffer and convert them to usable integers, do all of the necessary
processing, then write the whole buffer back to a new bmp file. This
would require only one write and one read. My experience with binary
character manipulation is, however, very limited and I have not yet
been able to pick out the individual bytes from buffer that I want.
Here's an example of how I'm trying it:
<******>
char buffer[25000000]; //buffer can handle a bmp up to 25MB
int fileSize;
int width;
ifstream bmp ("image.bmp", ios::binary); //open bmp for binary input
bmp.seekg(0, ios::end); //put cursor at end of file
fileSize = bmp.tellg(); //offset of last byte = size of file
bmp.seekg (0, ios::beg); //put cursor at beginning of file
bmp.read (buffer, fileSize); //read entire bmp into char string buffer
width = (int)buffer[18];
cout << width << endl;
<******>
Instead of setting the 18th, 19th, 20th, and 21st byte into "width", it
just sets the 18th byte by itself. I was hoping c++ would be smart
enough to realize that since "int width" was 4 bytes by definition, it
would know to fill in the other 3 appropriately. So my question is how
would I get all 4 bytes into "width" as an integer value.