Array pointer allocation?

Question

Array pointer allocation?

Referring to the comment line:

Why does adding parentheses in the example work to print the entire contents of the array?

The example prints “one,” then prints the garbage.

#include <iostream>

int main() {
    const char* a[3] = { "one", "two", "three" };
    const char*(*p)[3] = &a;
    for(int i = 0; i < 3; i++) {
        std::cout << *p[i] << std::endl; // this line
    }
    return 0;
}

It works after the change:

std::cout << (*p)[i] << std::endl;

+5

c ++ arrays pointers

thelittlegumnut Apr 15 '13 at 10:58

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4 answers

. () [] , dereferenced. () - dereference, [].

+6

ForEveR 15 . '13 11:00

operator priority .

Array selection has higher priority than dereferencing, so from a compiler point of view, this is valid:

*(p[i])

+2

Some programmer dude Apr 15 '13 at 11:00

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        #include <iostream>
        using namespace std;       

        int main() {


            int arr[5] = {1,2,3,4,5};

            int *p=arr;


            int intgerSize=sizeof(int);


            for(int k=0;k<5;k++)


            {  
                cout<<"arr ["<<k<<"] "<<*(p+(k*sizeof(int)/intgerSize));  
                cout<<"  "<<(p+(k*sizeof(int)/intgerSize));
                cout<<"  "<<p+k<<"\n"; 

            }`enter code here`

            return 0;
        }
OUTPUT:- 
arr [0] 1 0x7ffd180f5800  0x7ffd180f5800
arr [1] 2 0x7ffd180f5804  0x7ffd180f5804
arr [2] 3 0x7ffd180f5808  0x7ffd180f5808
arr [3] 4 0x7ffd180f580c  0x7ffd180f580c
arr [4] 5 0x7ffd180f5810  0x7ffd180f5810

+1

ankit gupta 12 sept '17 at 17:42

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Joseph Mansfield · Accepted Answer · 2013-04-15T11:03:23+0000

p is a pointer to an array of three elements, such as:

┌─────┬─────┬─────┐
│     │     │     │
└─────┴─────┴─────┘
   ^
   └─ p

Note that it points to the entire array, and not to one of its elements.

The expression is *p[i]considered as *(p[i])due to the priority of the operator (which is equivalent *(*(p + i))). This means that you are indexing a pointer to an array. If you do p[1], for example, you move the pointer to the "next" array and try to dereference it:

┌─────┬─────┬─────┐
│     │     │     │
└─────┴─────┴─────┘
                     ^
                     └─ p + 1

, , undefined. , (*p)[i] ( *((*p) + i)), , . , . , :

┌─────┬─────┬─────┐
│     │     │     │
└─────┴─────┴─────┘
   ^
   └─ *p

, . , , (*p)[1], :

┌─────┬─────┬─────┐
│     │     │     │
└─────┴─────┴─────┘
         ^
         └─ (*p) + 1

const char*, cout.

Array pointer allocation?

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