Convert pgm format image to pbm (black and white 0 or 1)?

#include <stdio.h>
#include <io.h>
#include <ctype.h>
 
// ...

FILE *pFile = fopen("result.pgm", "r");
// NOTE: With Microsoft compilers these functions might require a 
//  leading under score (_filelength, _fileno)
long file_len = filelength(fileno(pFile));
unsigned char *buffer = (unsigned char *)malloc(file_len);
fread(buffer, 1, file_len, pFile);
fclose(pFile);
 
const char *header = (const char *)buffer;
 
// Skip magic number "P4"
while (isalnum(*header)) header++;
// Skip white spaces
while (isspace(*header)) header++;
// Get width
int width = atoi(header);
// Skip width
while (isdigit(*header)) header++;
// Skip whitespace
while (isspace(*header)) header++;
int height = atoi(header);
// Skip height
while (isdigit(*header)) header++;
// Skip single whitespace
header++;
 
// Pointer to first data (pixel) byte
const unsigned char *data = (const unsigned char *)header;
// Extra byte per row if width is not a multiple of 8
int stride = width % 8;
for (int i = 0; i < height; i++)
{
    for (int j = 0; j < width / 8; j++)
    {
        unsigned data_byte = *data++;
        for (int k = 0; k < 8; k++)
        {
            // Maybe the order of bits is wrong here.
            // If so check with mask 0x80 and shift left.
            // EDIT: Black is 1 and white is zero!
            printf("%d,", (data_byte & 1) ? 0 : 255);
            data_byte >>= 1;
        }
    }
    if (stride)
    {
        unsigned data_byte = *data++;
        for (int k = 0; k < stride; k++)
        {
            // Again: Maybe the order of bits is wrong here.
            printf("%d,", (data_byte & 1) ? 0 : 255);
            data_byte >>= 1;
        }
    }
}
free(buffer);