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Passing a const object by reference.

 
 
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      01-28-2006
Hey all.

I just changed from this:

mat4& operator = (mat4 & mymat4);

to this:

mat4& operator = (mat4 const& mymat4);

all over my different classes, as some compilers compiled without the const, but I learned that it is necessary.

Now, I get this error:

binary '[' : no operator found which takes a left-hand operand of type 'const mat4' (or there is no acceptable conversion)

Here is the function implementation:

mat4& mat4:perator = (mat4 const& mymat4)
{
m[0] = mymat4[0]; m[4] = mymat4[4]; m[8] = mymat4[8]; m[12] = mymat4[12];
m[1] = mymat4[1]; m[5] = mymat4[5]; m[9] = mymat4[9]; m[13] = mymat4[13];
m[2] = mymat4[2]; m[6] = mymat4[6]; m[10] = mymat4[10]; m[14] = mymat4[14];
m[3] = mymat4[3]; m[7] = mymat4[7]; m[11] = mymat4[11]; m[15] = mymat4[15];
return *this;
}

And here is the definition of the [] operator:

float& mat4:perator [] (int subscript)
{
return m[subscript];
}

Anyone understand this error?


Thanks!



 
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Pete C
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      01-28-2006
<dontspam@_dylan_.gov> wrote:
> And here is the definition of the [] operator:
> float& mat4:perator [] (int subscript)
> {
> return m[subscript];
> }


You need to define another operator[], but const - like this:

const float& mat4:perator [] (int subscript) const
{
return m[subscript];
}

This version of the function will be called by the (const)
right-hand-side of all your assignments.
This may or may not compile - I don't know, because you haven't told us
the type of the 'm' member variable. But give it a try.

 
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