Binary to char converting in c - c

Question

I have been trying to convert a binary number into a char, I use the following code to convert the char into binary:
void bin(char x){
int y;
for(y = 0; y < sizeof(char) * 8; y++){
fprintf(f2,"%c", ( x & (1 << y) ) ? '1' : '0' );
}}
And it works fine.
The problem is that I don't know how to undo it, I want to get this binary number and convert it to the initial char. I'm using the folliwing code but it generates a core problem.
char subbuff[9];
memcpy( subbuff, &fichero[0], 8 );
subbuff[8] = '\0';
for(int k=8;k<fichero_len;k+=8){
char c = strtol(subbuff, 0, 2);
printf("%s = %c = %d = 0x%.2X\n", subbuff, c, c, c);
memcpy( subbuff, &fichero[k], k+8 );
subbuff[8] = '\0';
}
for exaple if i convert the string "hola" the first code shows "00010110111101100011011010000110"
but if i put that into the second code:
const char *hola="00010110111101100011011010000110";
char subbuff[16];
memcpy( subbuff, hola[0], 8 );
subbuff[8] = '\0';
for(int k=8;k<strlen(hola);k+=8){
char c = strtol(subbuff, 0, 2);
printf("%s = %c = %d = 0x%.2X\n", subbuff, c, c, c);
memcpy( subbuff, &hola[k], k+8 );
subbuff[8] = '\0';
}
it generates a core problem

Answer 1

EDIT 1:
One problem is that you are copying too many bytes into subbuff with
memcpy( subbuff, &fichero[k], k+8 );
Another is that you pass a bad pointer to memcpy with
memcpy( subbuff, hola[0], 8 );
which will cause a segfault. Please enable compiler warnings.
There is no need even to do that first, outside of the loop. It can be done similar like this
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void) {
const char *hola = "01101000011011110110110001100001";
char subbuff[9];
char result [256] = "";
unsigned char c;
int k;
int index = 0;
int fichero_len = (int)strlen(hola);
for(k = 0; k < fichero_len; k += 8) {
memcpy(subbuff, &hola[k], 8); // <--- copy 8 butes only
subbuff[8] = '\0';
c = (unsigned char)strtol(subbuff, 0, 2);
printf("%s = %c = %d = 0x%.2X\n", subbuff, c, c, c);
result[index++] = c;
result[index] = '\0';
}
printf("Result = %s\n", result);
return 0;
}
Finally your bit sequences are reversed, so you won't get the char back that you started with!
EDIT 2: after adding a few lines to the above code and reversing the bits in the hola definition, I get this output. Obviously you must make sure that result[] is long enough.
Program output:
01101000 = h = 104 = 0x68
01101111 = o = 111 = 0x6F
01101100 = l = 108 = 0x6C
01100001 = a = 97 = 0x61
Result = hola