why read as binary is different as xxd -b file and how to read as binary like xxd

Code:

#include <stdio.h> 
 
unsigned char mask = 1; 
unsigned char bits[8]; 
int main() 
{ 
unsigned char buffer[1000]; 
FILE *ptr; 
 
ptr = fopen("readasbinary.csv","rb");  // r for read, b for binary 
 
fread(buffer,sizeof(buffer),1,ptr); // read 10 bytes to our buffer 
 
int i = 0; 
int j = 0; 
for(i = 0; i<1000; ++i) 
{ 
 for (j = 0; j < 8; ++j) 
 { 
  bits[j] = (buffer[i] & (mask << j)) != 0; 
 } 
 for (j = 0; j < 8; ++j) 
 { 
  printf("%d", bits[j]); // prints a series of bytes 
 } 
 printf(" "); 
} 
 
FILE *write_ptr; 
 
write_ptr = fopen("readasbinary2.csv","wb");  // w for write, b for binary 
 
fwrite(buffer,sizeof(buffer),1,write_ptr); // write 10 bytes to our buffer 
}