What is malloc doing in this code?

Question

Could you explain following code?

str = (char *) malloc (sizeof(char) * (num+1));

1. What is malloc doing here?

Answer 1

sizeof(char)

is safe. One shouldn't assume a single byte per character.

My question is what are you doing programming if you don't know what malloc does?

man malloc

on a Linux system. On Windows. who knows? Probably 17 mouse clicks.