Imagine you have to initialize a big structure, that has a lot of members. If you don't zero-initialize it you have to manually initialize all the fields, one b

Imagine you have to initialize a big structure, that has a lot of members. If you don't zero-initialize it you have to manually initialize all the fields, one by one. Not only it takes a lot of lines of code that can be avoided, and it's less efficient to initialize all the zero fields than writing 0 in all the structure, but you can forget to initialize one and good luck debugging it. Or the structure can be modified by adding a optional field, that you have to remember to zero initialize everywhere you don't need it (instead of assuming it's zero because it's zero initialized). Of course accessing not initialized fields can lead to catastrophic bugs, imagine for example a structure containing a pointer not initialized to NULL that points to a random location, or a char* field that doesn't have a null-terminator in it. It's safer to 0 initialize everything, at least if you forgot to initialize something you have a predictable situation that is still better than the value of the field depending on what was there previously that is not deterministic.