Memset Definition and use

Question

What's the usefulness of the function memset()?.

Definition: Sets the first num bytes of the block of memory pointed by ptr to the specified value (interpreted as an unsigned char).

Does this mean it hard codes a value in a memory address?

memset(&serv_addr,0,sizeof(serv_addr) is the example that I'm trying to understand.

Can someone please explain in a VERY simplified way?

Answer 1

memset() is a very fast version of a relatively simple operation:

void* memset(void* b, int c, size_t len) {     char* p = (char*)b;     for (size_t i = 0; i != len; ++i) {         p[i] = c;     }     return b; } 

That is, memset(b, c, l) set the l bytes starting at address b to the value c. It just does it much faster than in the above implementation.

Answer 2

memset() is usually used to initialise values. For example consider the following struct:

struct Size {     int width;     int height; } 

If you create one of these on the stack like so:

struct Size someSize; 

Then the values in that struct are going to be undefined. They might be zero, they might be whatever values happened to be there from when that portion of the stack was last used. So usually you would follow that line with:

memset(&someSize, 0, sizeof(someSize)); 

Of course it can be used for other scenarios, this is just one of them. Just think of it as a way to simply set a portion of memory to a certain value.