printf, fprintf, sprintf and printk..... whats the difference ?

There are basically 3 standard "streams"

1. stdin - standard input stream
2. stdout - standard output stream
3. stderr - standard error stream

fprintf(standard stream, "message");  //message is sent to the mentioned stream

printf("message"); //message is sent to stdout. so it is as good as writing fprintf(stdout, "message")

#define BUFFER_SIZE 50

char *ch_arr = (char *)malloc(sizeof(char) * BUFFER_SIZE);

sprintf(ch_arr,  "message"); //message is sent to char buffer whose pointer is passed as argument

printk(KERN_IMERG "message");  

//used to print message to kernel log file. Hence it can only be called from kernel only