C printing binary data
After you have opened the binary file, you can read and write a structure or seek a specific position in the file. A file position indicator points to record 0 when the file is opened.
A read operation reads the structure where the file position indicator is pointing to. After reading the structure the pointer is moved to point at the next structure. A write operation will write to the currently pointed-to structure. After the write operation the file position indicator is moved to point at the next structure.
Remember that you keep track of things, because the file position indicator can not only point at the beginning of a structure, but can also point to any byte in the file.
Only one block is requested. Changing the one into ten will read in ten blocks of x bytes at once. In this example we declare a structure rec with the members x,y and z of the type integer. In the main function we open fopen a file for writing w. Then we check if the file is open, if not, an error message is displayed and we exit the program. Then we write the record to the file. We do this ten times, thus creating ten records.
Take a look at the example:. With the fread we read-in the records one by one. After we have read the record we print the member x of that record. The only thing we need to explain is the fseek option. The function fseek must be declared like this:.
The fseek function sets the file position indicator for the stream pointed to by the stream. The new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. Three macros are declared in stdio.
Using negative numbers it is possible to move from the end of the file. In this example we are using fseek to seek the last record in the file. This counter is then used in the fseek statement to set the file pointer at the desired record. The result is that we read-in the records in the reverse order. The function rewind can be used like this:. With the fseek statement in this example we go to the end of the file.
Then we rewind to first position in the file. Then read-in all records and print the value of member x. Without the rewind you will get garbage. The int types must contain at least 16 bits to hold the required range of values.
But it also can vary per compiler and the platform you are compiling for. On compilers for 8 and 16 bit processors including Intel x86 processors executing in 16 bit mode, such as under MS-DOS , an int is usually 16 bits and has exactly the same representation as a short. On compilers for 32 bit and larger processors including Intel x86 processors executing in 32 bit mode, such as Win32 or Linux an int is usually 32 bits long and has exactly the same representation as a long.
A int holds 32 bits thus you see 01 00 00 00 in your hex-editor. Try the following example to see the sizeof variable types for your target platform: So if you want to see only one byte in your hex editor, change the program to this: If you open the file test.
Or if you want to use int, accept that 4 bytes are written in the binary file but at least you know now why this is. Hi, after piratical and try to understanding write and read, my write is perfect what i want, but i can not read my bin file, i need some help please,.
I have tested them and they work, so good luck! Hi, Tanks for your help and support, my last message with my binary writer test, is perfect for me, because i can write a hex value directly in file , 00 to FF anywhere i want in file, but i cant read it with fread after, i want practice this with a small file i have create because my true application i want manage. Is this the right declaration of a binary file Binary files should have b in the mode e.
You are right, if you only look at the syntax. But if you open test. But to keep the syntax correct, we have changed the source code examples. The modes you can use are as follows: Is there a possibility to deal with data packing of the compiler in the structure, because due to this structure members are not necessarily continuous in the memory.
And mention that you get garbage without the rewind. If you seek to the end of file and then offset beyond the end of the file, you will be reading garbage, you need a negative offset. The search for the end of the file is only done, so we that we can rewind. I want to dump some memory into a file, a complex structure which contains pointers to list etc, and again want to set the same memory from this file. Try something like this: Above code is most certainly wrong.
Bit shifting does not rely on an architecture's endianity. Endianity has to do with how data is stored in memory. When operating on specific variables you can ignore it entirely. Compyx - thanks for correcting: But I also want to add or subtract them in binary format. But I also want to add or subtract them in binary format All numbers on your personal computer are stored as binary.
There is no such thing as base numbers other than what you may print to the screen, save to a file, or write on paper. There are no tools for displaying values in binary-format to the screen; you will need to develop this yourself.
Don't worry -- it's not rocket science level stuff. Here is one way to convert bit integers to binary for display: I've never seen a negative binary number represented with a minus sign. Where did you get this notion from? A signed-int value uses the most-significant bit to denote the sign of the value: And what is the purpose of the following which I do not think it yields the value you seek: Thus the number of characters necessary to store a 4-byte signed-int value in "binary format" will be 32 bytes plus an additional byte if you wish to form a string.
Just declare the value on the stack. You don't need to depend on the assumption that a byte is an octet. Because I print it, since printed text is read by humans, and not computers. I assume that anybody is intelligent enough to see that they need to fill the rest up with zero's if they want a 32 bit representation including adding the MSB.
But not using it sucks even more when anybody else but you needs to read your code. For example, if anybody passes a string parameter, you see right away whether it is unicode or not.