Data member, assigned once at runtime, const thereafter.

[BrowserUk]

Hi,

I have an int data member in a class that is assigned a value at instantiation and thereafter remains constant until destruction.

This data member, n, is the limit for a large number of loops, and the loop code generated is expensive because I can't mark it const:

; 150 : // invert Lower Triangle;
; 151 : for( int i=0; i < n; i++ ){

inc r9d
add rbx, 8
add r8, 8
cmp r9d, DWORD PTR [r11+56] <<< compare i < n
jl SHORT $LL13@MultPC
mov rbx, QWORD PTR [rsp+16]

Is there a way to mark n as const after it is assigned once?

(Note: this is of necessity MSVC9; thus circa C99)

Cheers.

[shadowmouse]

If it is only given a value at the instantiation of the class, can't you mark it as const and initialise it in the initialiser list of the constructor?

[BrowserUk]

Unfortunately not.

The object is populated with data from a file; n varies with the size of the file; but once loaded doesn't change.

n is then used as the bound in literally dozens of loops; and the code is indirecting for every iteration of every loop, rather than just loading the value into a register and comparing.

I can work around it by having

class::method ( ... ) {
    const int nn = n;

...

    for( int i=0; i < nn; ++ i ) {
        ...
    }
...
}

But as there are actually half a dozen of these limits for various loops I end up with something like this at the top of many methods:

const int NNumBlockLabels = NumBlockLabels, NNumNodes = NumNodes, NNumLineProps = NumLineProps, NNumEls = NumEls, NNumPBCs = NumPBCs;

which is less than nice :)

Cheers, Buk.