Programming_Micro_Note_20161012.md

Programming Micro Note 20161010

Returning array from pure C funcion

Source:
How to make an array return type from C function?

Q:
How do I return an array form pure C function?

char *makeArray(char array []) {
    char returned [10];
    //handling the array
    return &(returned[0]); //is this correct?
} 

like this perhaps?

A:
Not in that way. The array disappers after leaving the scope. You can use either the static variable or dynamically allocate them. Another way is to pass a pointer which points to an allocated memory to the function as a parameter.

Option 1:

char *makeArray(int count) {
    char *ret = malloc(count);
    if(!ret)
        return NULL;

    for(int i = 0; i < count; ++i) 
        ret[i] = i;

    return ret;
}

Option 2:

void makeArray(char *buf, int count) {
    for(int i = 0; i < count; ++i)
        buf[i] = i;
}

---

Dereference NULL pointer

Source:
Why dereferencing a null pointer is undefined behaviour? I do not know C

Q: What happens if I dereference a NULL pointer?
A: Undefined Behavior!
Q: But why UB instead of...?
A: Otherwise compiler needs to check if the pointer is NULL and take corresponding action. It may limit potential optimizations. See question 2 in I do not know C