Read File in Binary format

[Radix]

Hello!

Problem : I need to get the content from a file and then split it in binary blocks to use in a RSA Encryptation. And that block should use one specific number of bits that were got from the user.


Question :
I would like to know how can I read a file(from any format : .txt / .jpg / etc ) get the content and split it in binary blocks (like : 10101001011 )to send to the RSA encryptation function.


Until now I have been using something like this but without success:

For get the bits number from the user:

	
while(1)
	{
		printf("Insert one integer between 8 and 128 that is multiple of 8: \n");
		gmp_scanf("%Zd", bitNumber);
		x = mpz_get_ui(bitNumber);
		if( (x % 8) == 0 )
		{
			printf("This is one multiple of 8.\n");
			break;
		}
		printf("Error , not 8 multiple , press any key to digit another number.\n");
	}

for get the file content:

	if(( fp = fopen(inFile , "rb"))==NULL)
	{
		printf("Impossible to open file");
		exit(1);
	}
	fclose(fp);

How can I get the correct information from this fp?

Thank you in advance for your help

[msh]

(1) What's `gmp_scanf()` and `mpz_get_ui()`? You'll struggle to get answers to questions involving the use of non-standard libraries, unless someone is familiar with them, which would be a rather poor bet. If these are yours, show us how they are defined, if not, seek help from the particular library's community.
(2) `fread()` and `fseek()` mostly.

[Radix]

GMP is a free library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floating point numbers. There is no practical limit to the precision except the ones implied by the available memory in the machine GMP runs on. GMP has a rich set of functions, and the functions have a regular interface.

However this will not interpose with the code in this area.

[msh]

Are you sure you need those for getting a value whose upper range requirements can be met by `char`?

Processing a binary file would look something like this. Not sure if this will compile as I don't have a compiler handy, and there are bound to be bugs, but it should give you a rough idea on how it works.

size_t block_size = x / CHAR_BITS;  // read this many bytes
FILE *fp = fopen(input_file, "rb");
if (!fp) {
        fprintf(stderr, "FATAL: Could not open file %s\n", input_file);
        exit(EXIT_FAILURE);
}

unsigned char *block = malloc(block_size);
if (!block) {
        fprintf(stderr, "FATAL: Memory allocation failed\n");
        exit(EXIT_FAILURE);
}

size_t bytes_read;
while (1) {
        bytes_read = fread(block, 1, block_size, fp);
        // process the block here, it's binary data
        if (bytes_read != block_size) {
                if (feof(fp))
                        break;  // files has been fully read
                if (ferror(fp)) {
                        fprintf(stderr, "FATAL: Error reading file %s\n", input_file);
                        // release resources
                        exit(EXIT_FAILURE);
                }
        }
}
// rewind the file with `fseek()` if you intend to do any other processing on it

[c coder]

Well, why couldnt you just use c=fgetc(fp); (where c is a char). A char is commonly 8-bits in total depending on the compiler i guess. Now, when you have that character (or all of them) you can extract the number of bits you want thereafter by just combining them in a sequential order.

[vart]

Well, why couldnt you just use c=fgetc(fp); (where c is a char).

because fgetc returns an int for a reason. putting return value to the char before checking will prevent you from distinguishing EOF indicating error from valid read of 0xff