Cannot convert to `int' in initialization

[Alex Vinokur]

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
return 0;
}
---------------

--- Compilation ---

// GNU gcc/gpp 3.4.1

$ gpp foo.cpp
foo.cpp: In function `int main()':
foo.cpp:5: error: cannot convert `Foo' to `int' in initialization

-------------------

Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Alf P. Steinbach]

* Alex Vinokur:

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
return 0;
}

Much wrong, but the reason it doesn't _compile_ is that the assignment
'foo1 = foo2' produces a Foo value where a condition is required -- a
condition must be a value that can be implicitly converted to bool.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Jonathan Turkanis]

"Alex Vinokur" <al****@big-foot.com> wrote in message
news:30******** *****@uni-berlin.de...

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
The declaration

int i = 0, foo1 = foo2

declares two variables of type int: i and foo1. The first is initialized with
the value 0. The second is supposed to be initialized with the value foo2, but
there is not conversion from this value to an int.
return 0;
}

For fun, try:

#include <iostream>
#include <typeinfo>

struct Foo {
operator int() const { return 5; }
};

int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ) {
std::cout << "typeof foo1 = " << typeid(foo1).na me() << "\n";
std::cout << "foo1 = " << foo1 << "\n";
break;
};
return 0;
}

Jonathan

[Alex Vinokur]

"Alf P. Steinbach" <al***@start.no > wrote in message news:41******** *********@news. individual.net. ..

* Alex Vinokur:

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
return 0;
}

Much wrong, but the reason it doesn't _compile_ is that the assignment
'foo1 = foo2' produces a Foo value where a condition is required -- a
condition must be a value that can be implicitly converted to bool.

[snip]

for (int i = 0, foo1 = foo2; ; );
or
for (int i = 0, foo1 = foo2; i < 100; i++);

Why is a condition required for 'foo1 = foo2'?

--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Jonathan Turkanis]

"Alf P. Steinbach" <al***@start.no > wrote in message
news:41******** *********@news. individual.net. ..

* Alex Vinokur:

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
return 0;
}

Much wrong, but the reason it doesn't _compile_ is that the assignment
'foo1 = foo2' produces a Foo value where a condition is required -- a
condition must be a value that can be implicitly converted to bool.

I think you missed the fact that 0 and foo1 are separated by a comma.

Jonathan

[Alex Vinokur]

"Jonathan Turkanis" <te******@kanga roologic.com> wrote in message news:30******** *****@uni-berlin.de...

"Alex Vinokur" <al****@big-foot.com> wrote in message
news:30******** *****@uni-berlin.de...

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
The declaration

int i = 0, foo1 = foo2

declares two variables of type int: i and foo1. The first is initialized with
the value 0. The second is supposed to be initialized with the value foo2, but
there is not conversion from this value to an int.

Sorry & Thanks.

Of courcs, now it is OK.

struct Foo {};
int main ()
{
Foo foo1, foo2;
int i;
for (i = 0, foo1 = foo2; ; );
return 0;
}

return 0;
}

[snip]
--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Alf P. Steinbach]

* Jonathan Turkanis:

"Alf P. Steinbach" <al***@start.no > wrote in message
news:41******** *********@news. individual.net. ..

* Alex Vinokur:

What is wrong in program below?

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ); // Line#5
return 0;
}

Much wrong, but the reason it doesn't _compile_ is that the assignment
'foo1 = foo2' produces a Foo value where a condition is required -- a
condition must be a value that can be implicitly converted to bool.

I think you missed the fact that 0 and foo1 are separated by a comma.

Yes.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Alex Vinokur]

"Jonathan Turkanis" <te******@kanga roologic.com> wrote in message news:30******** *****@uni-berlin.de...
[snip]

For fun, try:

#include <iostream>
#include <typeinfo>

struct Foo {
operator int() const { return 5; }
};

int main ()
{
Foo foo1, foo2;
for (int i = 0, foo1 = foo2; ; ) {
std::cout << "typeof foo1 = " << typeid(foo1).na me() << "\n";
std::cout << "foo1 = " << foo1 << "\n";
break;
};
return 0;
}

[snip]

Indeed, very nice.
--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Andrew Koenig]

"Alex Vinokur" <al****@big-foot.com> wrote in message
news:30******** *****@uni-berlin.de...

Of courcs, now it is OK.

struct Foo {};
int main ()
{
Foo foo1, foo2;
int i;
for (i = 0, foo1 = foo2; ; );
return 0;
}

You could also have written it this way if you wanted to confuse people:

Foo foo1, foo2;
for (int i = foo1 = foo2, 0; ;) ;

PS: Don't try this for real, but do understand why it works.

[Alex Vinokur]

"Andrew Koenig" <ar*@acm.org> wrote in message news:8J******** ***********@bgt nsc05-news.ops.worldn et.att.net...

"Alex Vinokur" <al****@big-foot.com> wrote in message
news:30******** *****@uni-berlin.de...

Of courcs, now it is OK.

struct Foo {};
int main ()
{
Foo foo1, foo2;
int i;
for (i = 0, foo1 = foo2; ; );
return 0;
}

You could also have written it this way if you wanted to confuse people:

Foo foo1, foo2;
for (int i = foo1 = foo2, 0; ;) ;

PS: Don't try this for real, but do understand why it works.

GNU gpp 3.4.1 doesn't compile that.

--- foo.cpp ---
struct Foo {};
int main ()
{
Foo foo1, foo2;
for (int i = foo1 = foo2, 0; ;) ; // Line#5
}
---------------

--- Compilation ---
$ gpp foo.cpp
foo.cpp: In function `int main()':
for.cpp:5: error: cannot convert `Foo' to `int' in initialization
for.cpp:5: error: expected unqualified-id before numeric constant
for.cpp:5: error: expected `,' or `;' before numeric constant
--------------------

--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn