C/stdlib.h/strtoull
strtoull: similar to strtoul() except that it returns an unsigned long long int
Header file: #include <stdlib.h>
Declaration: unsigned long long int strtoull(const char *restrict start, char **restrict end, int radix);
#include <stdlib.h>
int main(void){
char *start, *end;
char a[100];
end = a;
*start= "12341234";
printf("%d", strtoull(start, &end, 8));
}