Confusing awkward array/struct syntax

**Chris87** · 01-02-2009

I've been taking notice of some extra syntactical feature that arrays and structs (probably other elements of C/C++ as well) have that aren't yet documented in your tutorials, nor any C/C++ books I've read.

Example 1:

Code:

struct
{
    int some_num;
    char[] some_string;
} my_instance = {0}

It seems normal up until the last line. What is this weird '= {0}' segment?

Example 2:

Code:

int some_multiarray[4][5] =
{{0,1,2,3,4},{0,1,2,3,4},{0,1,2,3,4},{0,1,2,3,4}}

I could probably guess this is some sort of initialization, but if so, are these initial values, or constant values?

**zacs7** · 01-02-2009

Ex1: Same as Ex2. Just with 0.
Note:

Code:

char[] some_string;

From Ex1 is illegal. Too much Java perhaps? :-)

Ex2: Yes, initial values (there is no const modifier in the declaration).

**Chris87** · 01-02-2009

Oh, it's just an example variable to fill the example struct with, no significance really... But that does work for me, though I've only tested a static char array.

EDIT: Also, speaking of initial values in a struct, would this be valid? ((using the bool type fdrom C++ in this one))

Code:

struct
{
    int number;
    bool status;
} something = {5, false}

**laserlight** · 01-02-2009

Originally Posted by Chris87

But that does work for me, though I've only tested a static char array.

What is the exact program that you tested? Which compiler did you use?

EDIT:

Originally Posted by Chris87

Also, speaking of initial values in a struct, would this be valid? ((using the bool type fdrom C++ in this one))

In C99, with <stdbool.h> included and with a terminating semi-colon, yes.

**Chris87** · 01-02-2009

MinGW GCC 3.4.5

**laserlight** · 01-02-2009

Originally Posted by Chris87

MinGW GCC 3.4.5

That should fail to compile your first example code and should spew out a number of error messages.

**Chris87** · 01-02-2009

Bugger... I'd use TDM's GCC 4.3.2 but I use toolkits like wxWidgets and what not that assume since I'm using MinGW32, I use 3.4.5... I think...

**laserlight** · 01-02-2009

Um, the problem is not with the compiler, the problem is with the code, as zacs7 stated. The second example is fine, once you add the terminating semi-colon.

**Chris87** · 01-02-2009

Hmm... see, when I did it with an uninitialized pointer, it crashed, but when I did something like:

Code:

char name[16];

It was ok.

**brewbuck** · 01-02-2009

Originally Posted by Chris87

Hmm... see, when I did it with an uninitialized pointer, it crashed, but when I did something like:

Code:

char name[16];

It was ok.

That's because a char[16] is absolutely nothing like an uninitialized char *

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