char array[] weird output

Question

char a[] = {'k','l','m'};
cout << a << endl;

int b[] = {1,2,3};
cout << b << endl;

I run the above C++ code and here's the output:

klm
0x22fe00

I observe that char is the only primary type that has this behavior. Why this is happening? Are there any specialities of the char type?

...I'd say you're lucky the compiler _just_ prints `klm` in this case, as `a[]` is not null-terminated. — celticminstrel, Jul 08 '15 at 15:05
I thought the compiler puts automatically null after the end of the array. — Kostas Lek, Jul 08 '15 at 15:22
It does if you use the string syntax: `char a[] = "klm";`. I'm pretty sure it doesn't when you use the array syntax. — celticminstrel, Jul 08 '15 at 15:25

score 1 · Answer 1 · answered Jul 08 '15 at 13:53

The name of an array often evaluates to the address of its first element. The standard output stream interprets character pointers as strings, and prints the data as a string. For integers, there is no such interpretation so you see the actual pointer value.

score 1 · Answer 2 · answered Jul 08 '15 at 13:55

1

The char[] is essentially how C and C++ treat strings of characters. The operator<< has been overloaded for the char[] to print out the values of the char array. On the other hand, arrays are essentially treated as constant pointers to their base element:

const int* p = &b[0];

Therefore, when you do cout << b << endl, you're actually printing out the base address of the array. That's why you get the hex number.

answered Jul 08 '15 at 13:55

Bizkit

384
1
10

Actually it's overloaded for `char*`, but, close enough. – Lightness Races in Orbit Jul 08 '15 at 15:06

char array[] weird output

2 Answers2