Printing in hex

[stubbsy]

Hi!
I'm composing the header for a wav file, and I need to insert the filesize. I have used

fseek (input_pointer , 0 , SEEK_END);  // 
long source_size = ftell(input_pointer);    // Obtain the length of the file  

to find the filesize.

I need to insert the filesize into the header in the format shown below

EG 96,000 is 0x017700 so written as 0077 0100 (in hex viewer).

How do I do this? I can't find the correct formats to go from the int32 to... whatever is necessary.

[edit] using fprintf...

One further exmaple. If the value was 192,000 it would need to be written such that it appeared as 00ee 0200 in a hex viewer.

thanks,
Paul

[helios]

Is that space in the middle necessary? If it is, you'll need to implement you own dec to hex conversion. Either that or insert it yourself in the buffer.

[stubbsy]

thank you for your reply.
no, the space isn't necessary, it's just the way it copied and pasted from my hex viewer.
it's worth noting that i don't actually need to write anything in hex, but the hex viewer i am using is only to help understand the way the characters have been rearranged.

[helios]

Oh, I see. Your question is why the order of the bytes changed, then?

[stubbsy]

no, not why, but how do i do it

[Corpus]

Don't have much time, but here's a quick bet:

Put your number in a string stream, create a string from it, get bytes from it and output them to file in reverse order. Would that work?

stringstream ss;
string s;
string bytes[4];
ofstream headerfile
// Open file etc.
ss << hex << setfixed(8) << filesize;
s = ss.str();

for(int i=0; i<4; i++)  bytes[i] = s(s.begin()+2*i, s.begin()+2*(i+1));
for(int i=3; i<=0; i--)  headerfile << bytes[i];

Remember to #include iomanip. I'm not sure of it, but something along these lines should work...

[helios]

You need invert the endianness of the integer.
For example, suppose you wanted to invert the endianness of a 16-bit integer:

int16 x=?;
int16 y=(x<<8)|(x>>8);

For more bits, you will need to do some bit twiddling. Just remember that (0x12345678 & 0x0000FF00)==0x00005600.