Re: dynamically allocating on the stack

[Timon Gehr via Digitalmars-d-learn]

On 21.04.2018 12:08, Giles Bathgate wrote:
On Saturday, 21 April 2018 at 07:57:41 UTC, Uknown wrote:
The language itself doesn't have something, but you could use `alloca`

I don't know if this little template function makes life easier:

------
pragma(inline, true)
ref T push(T)(size_t len)
{
     import core.stdc.stdlib, core.stdc.stdio;

     return *cast(T*)alloca(T.sizeof * len);
}


void doSomething(size_t len)
{
     auto stackBuffer = push!char(len+1);
     stackBuffer[0] = 'H';
     stackBuffer[1] = '\0';
     printf("%.*s", stackBuffer.ptr);
}

void main()
{
     doSomething(2);
}
------



That does not work (you are returning a dangling reference into the 
stack of the function that is returning). You could do this:

import core.stdc.stdlib, core.stdc.stdio;
auto push(T,alias len)(T[] mem=(cast(T*)alloca(T.sizeof*len))[0..len]){
    return mem; // (uninitialized!)
}
void doSomething(size_t len){
    char[] stackBuffer=push!(char,len);
    stackBuffer[0] = 'H';
    stackBuffer[1] = '\0';
    printf("%s", stackBuffer.ptr);
}

void main(){
    doSomething(2);
}