CODEWITHSUNDEEP
c++arraystypes
DarkTrick
DarkTrick

Reputation: 3467

C++: Type of multidimensional array with `variable` size

I can run this

int a = 5; 
auto foo = new int [a][4][4];

But when I try this:

int a = 5; 
int * foo[4][4];
foo = new int [a][4][4];

I get the error

error: incompatible types in assignment of ‘int (*)[4][4]’ to ‘int* [4][4]’

Question

What type do I have to specify for foo?

Edit: The goal is to have one single chunk of memory, not an array of pointers.

Upvotes: 2

Views: 81

Answers (2)

StefanKssmr
StefanKssmr

Reputation: 1226

As @john correctly identified:

You're confused between a 2D array of pointers (that's what you wrote) and a pointer to a 2D array (that's what you want).

So what's the difference between pointer to an array and array of pointers. The correct syntax to define a pointer to an array (what you tried to do):

data_type (*var_name)[array_size];

But this defines an array of pointers (what you actually did):

data_type *var_name[array_size];

@OP in your own answer you already found out what the correct type should be – a pointer to an array int (*foo)[4][4], but I thought a little more explanation is also helpful.

Upvotes: 2

DarkTrick
DarkTrick

Reputation: 3467

The error message is a little confusing because it does not state the variable name.

This works:

int a = 5; 
int (*foo)[4][4];
foo = new int [a][4][4];

Upvotes: 3

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