Unable to calc the 'sizeof' of a member of struct (pointers problem?)

[tonnot]

I have this 2 functions

myfunction1 (myclass &value)
myfunction2 (int &value)

I want to pass the values by ref to avoid copies.
Ok, I have a object created like this
a_struc * my_struc= new a_struc;
(a_struc is a simple struct with 3 fields, the third is an int field called a3. )

myfunction1(*mystruc) works
myfunction2(*mystruc->a3) does not compile
myfunction2(mystruc->a3) compile, but inside myfunction2 I have :
int si = sizeof value; and in this last case I have an error ....(programs crash)

Any help? Thanks

[stampede]

I want to pass the values by ref to avoid copies.

Passing an int by reference is not going to give you some incredible increase in app performance :P
btw if arguments are meant to be read-only, pass them by const reference ( for classes and structs ) or value (ints, doubles etc )

myfunction2(*mystruc->a3) does not compile

Correct syntax would be myfunction2(mystruc->a3) or myfunction2((*mystruc).a3), but I think you've already figured it out.

but inside myfunction2 I have :
int si = sizeof value; and in this last case I have an error ....(programs crash)

Make sure pointer is not deleted before function call, this works ok:

#include <iostream>
 
struct my_struct{
	int x, y, z;
};
void method( int x ){ // or by reference int &x, works as well
	std::cout << sizeof x << "\n";
}
void method( const my_struct& s ){
	std::cout << sizeof(s) << "\n";
}
int main( int argc, char ** argv ){
	my_struct * s = new my_struct;
	method((*s).x);
	method(s->x);
	method(*s);
	delete s;
	return 0;
}

#include <iostream>

struct my_struct{
	int x, y, z;
};
void method( int x ){ // or by reference int &x, works as well
	std::cout << sizeof x << "\n";
}
void method( const my_struct& s ){
	std::cout << sizeof(s) << "\n";
}
int main( int argc, char ** argv ){
	my_struct * s = new my_struct;
	method((*s).x);
	method(s->x);
	method(*s);
	delete s;
	return 0;
}

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[mcosta]

In myfunction1 and 2 value is a reference to myclass and integer so sizeof returns 4 for 32bit or 8 for 64bit

This code

#include <QCoreApplication>
 
struct MyStruct
{
    int a3;
};
 
void myfunction1 (MyStruct &value)
{
    int si = sizeof (value);
 
    qDebug ("[%s]: Sizeof = %d", Q_FUNC_INFO, si);
}
 
void myfunction2 (int &value)
{
    int si = sizeof (value);
 
    qDebug ("[%s]: Sizeof = %d", Q_FUNC_INFO, si);
}
 
int main (int argc, char* argv[])
{
    QCoreApplication a (argc, argv);
 
    qDebug ("Hello World");
 
    MyStruct *ms = new MyStruct;
 
    myfunction1 (*ms);
 
    myfunction2 (ms->a3);
 
    delete ms;
}

#include <QCoreApplication>

struct MyStruct
{
    int a3;
};

void myfunction1 (MyStruct &value)
{
    int si = sizeof (value);

    qDebug ("[%s]: Sizeof = %d", Q_FUNC_INFO, si);
}

void myfunction2 (int &value)
{
    int si = sizeof (value);

    qDebug ("[%s]: Sizeof = %d", Q_FUNC_INFO, si);
}

int main (int argc, char* argv[])
{
    QCoreApplication a (argc, argv);

    qDebug ("Hello World");

    MyStruct *ms = new MyStruct;

    myfunction1 (*ms);

    myfunction2 (ms->a3);

    delete ms;
}

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executes without crash with output

Hello World
[void myfunction1(MyStruct&)]: Sizeof = 4
[void myfunction2(int&)]: Sizeof = 4

Hello World
[void myfunction1(MyStruct&)]: Sizeof = 4
[void myfunction2(int&)]: Sizeof = 4

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[tonnot]

I'm going to stop ....
I hope to solve this tomorrow ...
There is something strange, I dont know where is the problem but code that works fine (as the examples you have showed) does not work into my classes ...
Thanks in any way.

[SixDegrees]

sizeof() is often implemented as a macro, and requires parentheses around the argument. Your psuedo-code doesn't do this; if your code doesn't, that's likely the problem.

[mcosta]

post you code