C++ zero init an array of templates with variable array length

Question

Is there a way to zero init an array of any type with a variable size? So what I want is to apply something like this:

int results[5] = {};

to a template like this:

T results[i] = {};

When I try this, my compiler says this: 'results' declared as array of functions of type 'T ()'. When I use any fixed typename I get this error: Variable-sized object may not be initialized

Also i is a variable that is passed in when this function is called.

Variable length arrays are not supported by C++ standard. Array size must be known during compilation. So, am not sure what you are asking about. — Algirdas Preidžius
– Algirdas Preidžius, Commented Dec 19, 2019 at 21:10
@AlgirdasPreidžius I don't know what you mean, I used T results[i]; without any problem... — user11914177
– user11914177, Commented Dec 19, 2019 at 21:11
If you are using gcc as your compiler, add -pedantic to your compiler options. — NathanOliver
– NathanOliver, Commented Dec 19, 2019 at 21:12
@user11914177 That's the point. T results[i] is a run time sized array and those are not allowed in C++. clang and gcc by default have an extension that lets you do it, but it is non-standard behavior. By using -pedantic you turn that feature off and tell the compiler to strictly follow the C++ standard. — NathanOliver
– NathanOliver, Commented Dec 19, 2019 at 21:16

Brian Bi · Accepted Answer · 2019-12-19 21:29:02Z

2

Variable-length arrays are non-standard in C++, and your compiler supports them as an extension. Your compiler also told you the limitations of the extension: the variable-length array may not have an initializer. As a work-around, you could do this:

int results[i];
std::fill(results, results + i, 0);

Of course, the better way is to use std::vector so you are not relying on any non-standard extensions.

answered Dec 19, 2019 at 21:29

Brian Bi

122k13 gold badges197 silver badges352 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

C++ zero init an array of templates with variable array length

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related