C++ 2d array initialization

Question

The following line doesn't work:

int n1=10,v1=10;  
int f[n1][v1]={};
error: variable-sized object ‘f’ may not be initialized

But the line below works, why?

const int n1=10,v1=10;  
int f[n1][v1]={};

In the first, `f` is a variable-length array. Those cannot be initialised. In the second, it's not a VLA, hence can be initialised. — Daniel Fischer, May 08 '13 at 21:27
See http://stackoverflow.com/questions/1887097/variable-length-arrays-in-c for a discussion of why you are limited to fixed length arrays — OOhay, May 08 '13 at 21:30

score 2 · Accepted Answer · answered May 08 '13 at 21:23

2

Array initializers need to be const.

An int value can change where as a const int value will remain constant throughout the entire program.

answered May 08 '13 at 21:23

Connor Hollis

I see, Could I put const int parameters? void test1(const int& n){ int f0[n]; int f1[n]={}; for(int i=0; i – wenfeng May 08 '13 at 21:38
It doesn't seem so, this was tested with G++ 4.5.3 under Cygwin: http://codepaste.net/gwnck4 – Connor Hollis May 08 '13 at 21:48

score 0 · Answer 2 · answered May 08 '13 at 21:23

0

In the second example, n1 and v1 are known to be compile-time constants. In the first example, they may not be.

answered May 08 '13 at 21:23

Marc Claesen

2 Answers2