Writing a stream of 9 bit values as bytes to a file in C

Question

I have an array with integer values from 0-511 (9 bits max). I am trying to write this to a file with fwrite.

For Example, with the array:

[         


        

Answer 1

Ok, so did it using bit shifting, oring (can also do with *, '+', % and /) but shift is more appropriate / readable, imo.

// Your data, n is the number of 9-bits values
uint16_t dat[] = { 257, 258, 259 };
int i,n = sizeof(dat)/sizeof(*dat);

// out file
FILE *fp = fopen("f8.bin","w");

uint16_t one = 0;
int shift = 0;
uint8_t b;

// main loop
for(i=0 ; i>(8-shift);     // Move the remaining MSb to the right
    shift = (shift+9) % 8;       // next shift
    fwrite(&b, 1, 1, fp);        // write our b byte
}
// remainder, always have a remainder
fwrite(&one, 1, 1, fp);
fclose(fp);

Had fun :-)