Setting an array pointer to null on declaration

Question 1

How can I set an array pointer tonull?

I have a pointer to a 3 int array that I am trying to set tonull.

int (*EXCLUSIVE_COLOR)[3];

Per this link I was trying to set it to null upon initialization.
However this does not assign a null value to it. It assigns three 'random' integers to the array elements:

{128, 447, 451}

How can I make it point to anull orempty value?

Question 2

if you assign null, test it for null, not read it

Question 3

What were you expecting to get when you read a null pointer? That's undefined behavior. It could give you anything. If you want to make the thing pointed to zero then do that. That's not the same as assigning a null pointer.

Question 4

Does this answer your question?Assigning an element of a multidimensional array to a second array

Question 5

Here is a full example that shows you all thing things you have been asking over the past few days:

int colors[][3] = {    {255, 0, 0},    {0, 255, 0},    {0, 0, 255}};#define NCOLOR (sizeof(colors) / sizeof(colors[0]))int *EXCLUSIVE_COLOR = NULL;void setup() {    Serial.begin(115200);    Serial.print("You have ");    Serial.print(NCOLOR);    Serial.println(" colors defined.");    reportColor();    EXCLUSIVE_COLOR = colors[2];    reportColor();    EXCLUSIVE_COLOR = NULL;    reportColor();}void loop() {}void reportColor() {    if (!EXCLUSIVE_COLOR) {        Serial.println("Color is not set");    } else {        Serial.print("Color is set to ");        Serial.print(EXCLUSIVE_COLOR[0]);        Serial.print(",");        Serial.print(EXCLUSIVE_COLOR[1]);        Serial.print(",");        Serial.println(EXCLUSIVE_COLOR[2]);    }}

You have an array of colours. You have a pointer that can point at a colour or at nothing. It starts off pointing at nothing. The code recognises that it's pointing at nothing and reports it. It gets assigned to a specific colour in your colours array. The code recognises that it's now a valid value and reports it. The pointer then gets pointed to nothing again. Again the code recognises that and tells you.

The result:

You have 3 colors defined.Color is not setColor is set to 0,0,255Color is not set

Majenko 106k5 gold badges82 silver badges139 bronze badges · Accepted Answer · 2020-06-10 17:13:47Z

Here is a full example that shows you all thing things you have been asking over the past few days:

int colors[][3] = {    {255, 0, 0},    {0, 255, 0},    {0, 0, 255}};#define NCOLOR (sizeof(colors) / sizeof(colors[0]))int *EXCLUSIVE_COLOR = NULL;void setup() {    Serial.begin(115200);    Serial.print("You have ");    Serial.print(NCOLOR);    Serial.println(" colors defined.");    reportColor();    EXCLUSIVE_COLOR = colors[2];    reportColor();    EXCLUSIVE_COLOR = NULL;    reportColor();}void loop() {}void reportColor() {    if (!EXCLUSIVE_COLOR) {        Serial.println("Color is not set");    } else {        Serial.print("Color is set to ");        Serial.print(EXCLUSIVE_COLOR[0]);        Serial.print(",");        Serial.print(EXCLUSIVE_COLOR[1]);        Serial.print(",");        Serial.println(EXCLUSIVE_COLOR[2]);    }}

You have an array of colours. You have a pointer that can point at a colour or at nothing. It starts off pointing at nothing. The code recognises that it's pointing at nothing and reports it. It gets assigned to a specific colour in your colours array. The code recognises that it's now a valid value and reports it. The pointer then gets pointed to nothing again. Again the code recognises that and tells you.

The result:

You have 3 colors defined.Color is not setColor is set to 0,0,255Color is not set

Movatterモバイル変換

Stack Exchange Network

Setting an array pointer to null on declaration

1 Answer1

Your Answer

Sign up orlog in

Post as a guest

Linked

Related

Hot Network Questions

Subscribe to RSS